Fiat 124 User Manual

Engine Maintenance and Modification

Bradley Artigue

1st Edition

Engine Maintenance and Modification

Bradley Artigue

1st Edition

Engine Maintenance + Modification

FIAT 124 Spider

Contents

1. Introduction ......................................................................................................................................................5

2. Concepts............................................................................................................................................................6

2.1 The Otto Cycle .............................................................................................................................................6

2.2 Lambda ........................................................................................................................................................6

2.3 Carburetor ....................................................................................................................................................7

2.4 Fuel Injection (FI or EFI) ...............................................................................................................................7

2.5 Compression Ratio (CR)...............................................................................................................................7

2.6 Home Mechanic...........................................................................................................................................8

2.7 Shop Manuals and Guides ...........................................................................................................................8

3. Engine Identification ........................................................................................................................................9

4. Carburetion .....................................................................................................................................................11

4.1 Understanding Carburetors ........................................................................................................................11

4.2 Air Bleed Correction...................................................................................................................................12

4.3 Idle Speed Control .....................................................................................................................................13

4.4 Transition....................................................................................................................................................13

4.5 Acceleration Pump .....................................................................................................................................14

4.6 Cold Starting...............................................................................................................................................15

4.7 Multi-Barrel Synchronization ......................................................................................................................16

4.8 Carburetor Identification and Schematics ..................................................................................................18

4.9 Carburetor Tuning ......................................................................................................................................35

4.10 Diagnostics and Troubleshooting .............................................................................................................36

5. Fuel Injection...................................................................................................................................................38

5.1 Fuel injection Basics ..................................................................................................................................39

5.2 The Air Flow Meter and Fuel Pump ...........................................................................................................40

5.3 Cold Starting Components.........................................................................................................................41

5.4 Warm-Up Components ..............................................................................................................................42

5.5 Idle Speed Control Components ................................................................................................................42

5.6 Cruising, Accelerating, and Deceleration Modes .......................................................................................43

5.7 The Oxygen Sensor ...................................................................................................................................44

5.8 Other Components ....................................................................................................................................44

5.9 Component Reference...............................................................................................................................45

5.10 Fuel Injection Tuning................................................................................................................................48

5.11 Fuel Injection System Electrical Diagrams...............................................................................................50

5.12 Fuel Injection System Part Numbers .......................................................................................................53

5.13 Diagnostics and Troubleshooting .............................................................................................................54

6. The Cylinder Head ..........................................................................................................................................59

6.1 Cylinder Head Identification .......................................................................................................................61

7. Intake Manifolds .............................................................................................................................................63

8. Exhaust System..............................................................................................................................................64

8.1 Exhaust System Identification ...................................................................................................................64

9. Ignition ............................................................................................................................................................66

9.1 Ignition Components..................................................................................................................................66

9.2 Ignition System Identification ....................................................................................................................67

9.3 Ignition Advance ........................................................................................................................................68

9.4 Firing Order and Initial Timing ....................................................................................................................69

9.5 Ignition Electrical Diagrams........................................................................................................................72

3

Engine Maintenance + Modification

9.6 Diagnostics and Troubleshooting ...............................................................................................................74

10. The Major Tune Up.......................................................................................................................................76

10.1 Preparation...............................................................................................................................................76

10.2 Tuning Procedure.....................................................................................................................................79

11. Improvements*.............................................................................................................................................80

11.1 Cylinder Head Improvements ..................................................................................................................81

11.2 Intake Manifolds ......................................................................................................................................84

11.3 Ignition .....................................................................................................................................................84

11.4 Exhaust and Emissions Control ...............................................................................................................86

11.5 Carburetors ..............................................................................................................................................87

Figures .................................................................................................................................................................89

Tables ..................................................................................................................................................................90

FIAT 124 Spider

Copyright © 2007 Bradley James Artigue.

All Rights Reserved.

This guide and others in this series are for educational purposes. All are freely distributable in their original,
unedited, and complete form. The online home of this document is www.artigue.com/fiat

.

4

Engine Maintenance + Modification

FIAT 124 Spider

1. Introduction

Welcome to my guide on FIAT 124 Spider engine maintenance and modification.
Spiders are great cars, born in the mid 1960's when sports cars were fun to drive,
affordable, and easy to work on. They remain a hobbyists’ dream. In 2002 I started to
compile the various pieces of knowledge I obtained over the years into guides, first on
carburetion and intake/exhaust systems, then, in 2004, a guide (more like a pamphlet) on
fuel injection. I revised both guides over the years and finally compiled everything into
this single document. My goal is to help you enjoy your FIAT as much as I enjoy mine.

Acknowledgements and great thanks to…

Jennifer Artigue, who has always supported (or tolerated) my obsession with
these cars;

Richard Ridge reviewed this guide several times throughout its development and
has been instrumental in reviewing my other works as well;

Eli Caul maintains Mirafiori, the FIAT page (www.mirafiori.com
tirelessly in his support of the FIAT community;

Andrew Artigue disassembled, rebuilt, restored, and drove many Spiders with
me throughout the last ten or so years;

Troy McKaskle performed the final edits on the document and allowed his cars
to be as test cases long before any of us claimed to know what we were doing;

Pete Angel supplied diagrams and suggestions and reviewed sections of this
document throughout its development;

and Mike Richmond and Thad Kirk who wrote or reviewed sections of my
previous works, much of which was brought over to this document.

Thank you for keeping these cars on the road.

September 2007

) and has worked

5

Engine Maintenance + Modification

FIAT 124 Spider

2. Concepts

This section describes some of the basic things we’ll discuss throughout this guide.

2.1 The Otto Cycle

The most common type of operation for automotive engines is the four-stroke cycle, also
known as the Otto cycle. Conceptualized in the 1870's by Nicolaus Otto (and others),
the cycle has four stages of operation, beginning with the engine at Top Dead Center
(TDC), when the piston is furthest from the crankshaft:

• Intake: The intake valve opens and fuel and air are drawn into the engine as the

piston is drawn down.

• Compression: The intake valve is closed and the piston rises, compressing the

mixture.

• Power: The compressed mixture is ignited, the resulting explosion forces the

piston down.

• Exhaust: The exhaust valve opens and the spent gases are forced out as the

piston rises.

If you want to know more about the Otto Cycle theory and all of the mechanical
engineering concepts that are involved pick up a copy of “A Practical Treatise on the
‘Otto’ Cycle Gas Engine” by William Norris, Longman, Green, and Co., London, England,

1896. At the time of this writing it is available for download on books.google.com. It is a
very old book but is wonderful at describing the basic concepts of an automobile engine.

2.2 Lambda

Fuel Injection systems and Carburetors have a common goal – to reach an air to fuel ratio
of 14.7:1 and maintain that ratio through changing engine loads. The ratio is known as
the stoichiometric air-fuel ratio for gasoline. It is commonly referred to as lambda. Any
mixture less than 14.7:1 is considered rich; any mixture above is considered lean.

The air fuel mixture is established on a carburetor by setting mechanical devices, such as
air bleeders, fuel jets, and emulsion tubes. On a fuel injection system the mixture is
constantly adjusted by a computer that varies the amount of fuel sprayed into the
cylinder. Both systems rely on a stream of measured air, regulated by a throttle, to
deliver atomized fuel into the engine.

6

Engine Maintenance + Modification

FIAT 124 Spider

2.3 Carburetor

A carburetor is a device that mixes fuel and air together for use in an internal combustion
engine. A throttle regulates the amount of airflow into an engine and the subsequent
increase in air speed and drop in pressure. A restriction in the carburetor barrel, known
as a venturi, forces the air stream to increase in speed as it passes by a number of fuel­delivering orifices. The orifices enrich the stream of air with fuel. The resulting mixture
is a near lambda combination of air and fuel.

2.4 Fuel Injection (FI or EFI)

A fuel injection system delivers a metered amount of fuel under high pressure into a
stream of air. Unlike carburetion, fuel injection does not rely on the pumping of the
engine to draw fuel into the air stream. Instead the fuel is forced through a small orifice
(a fuel injector) at very high pressure. The flexibility of fuel injection systems and
accuracy of fuel delivery leads to increased horsepower, better atomization of fuel,
reduction in emissions, and improved fuel economy.

2.5 Compression Ratio (CR)

The compression ratio is used to measure the performance of an internal combustion
engine. The compression ratio is calculated by taking the cylinder bore (diameter), piston
stroke, and volume of the combustion chamber prior to ignition. The formula looks like
this:

Where b is cylinder bore diameter, s is the piston stroke length, and Vc is the volume of

the combustion chamber. It is important to note that your author inserted this only to
demonstrate use of the pi (π) character and because formulas make guides like this one
look more scientific and authoritative.

FIAT Spiders had compression ratios that ranged from a low of 7.5:1 (Spider Volumex) to
a high of 9.8:1 (124 Sport Spider 1608). The Volumex relied on a supercharger to
increase the horsepower of the engine; therefore, it is notable that compression ratios
alone are not the sole indication of an engine’s capabilities. Generally speaking, and
since most of us would not install (and could not find) a Volumex supercharger on our
FIAT, mild increases in CR towards the 9.8:1 range result in good performance
increases. CR is typically increased with a piston swap, although other methods
(described later in this guide) will bump it up a point or two.

Pistons are available that will drive the CR of the engines upwards, all the way to 11:1. A
general rule about compression ratios is that the higher the CR the higher octane fuel

7

Engine Maintenance + Modification

you will need to keep the engine from knocking. These days most FIATs are recreational
vehicles, and pump-grade ‘super’ unleaded of 92 or higher octane will satisfy the CR of
any stock Spider up to 9.8:1.

FIAT 124 Spider

2.6 Home Mechanic

Throughout this guide I make references to the “home mechanic.” This is, most likely,
you. As these cars age finding a qualified professional mechanic is becoming more and
more difficult. Spiders are easy to work on and, with few exceptions, will not require
any specialized tools to make run correctly. Your best source for diagnostics is yourself;
if you must use a professional mechanic arm yourself with the ability to discuss the
problem.

2.7 Shop Manuals and Guides

A “shop manual” is referred to many times in this guide. There is only one shop manual
for your car, it was originally published by FIAT and is sold by FIAT parts vendors. There
were also numerous “guides” published by companies like Autobook, Haynes, Chilton’s,
and Drake. To avoid any confusion please note that unless explicitly stated, references
to the shop manual always indicate the FIAT shop manual.

8

Engine Maintenance + Modification

FIAT 124 Spider

3. Engine Identification

It is important to know what engine, cylinder head, carburetor, intake manifold, and
exhaust system you have on your FIAT. Understanding what you have allows you to
make an educated decision about what you need. If you are not 100% sure of what you
have then take a few moments to check - many have had engine, cylinder head,
carburetor, exhaust, ignitions, and all kinds of other parts swapped out. You need to
know what you’re running in order to get it running right or swap it for the right thing.

The engine identification number is stamped into the engine block near the oil filter. It is
sometimes covered in grime. Carburetor cleaner or degreaser and a brush will allow you
to read it. On the Spider 2000 engine (1979-1985) it is located just to the right of the oil
filter. On all Spiders manufactured prior to 1979 it is located above the oil filter. Check
your engine number with the chart on the next page. It is important to note that the last
few numbers may not match up - this usually indicates an engine swap at some point in
your car’s history. If the first digits (i.e. 132A1 is always a 1756) are correct then you
have the original displacement engine in your vehicle. If the last few digits (i.e. 031.5)
are correct then you have the original displacement and model year type.

Figure 1: Engine Identification

What if you don’t have the original engine? This situation is more common than you
might think – many owners installed larger motors to gain additional performance, a
common swap was the 1608cc for the 1438cc. Others had swaps due to necessity,
such as installing a 1978 engine in their 1975 because the original no longer worked.
Whether or not a swap was good is something you need to decide for yourself; if
originality is your goal then it may be worthwhile to seek out the original parts. If power
is more important then it might be worth keeping that 102 HP 1608cc instead of
installing a 91 HP 1438cc.

9

Engine Maintenance + Modification

Table 1: Engine Identification Table

Model Year Series From S/N Engine Displacement

1967 – 1969 124AS 5619 124AC.040 1438cc

1970 – 1971 124BS 21861 124AC.040 1438cc

1971 - 1972 124BS1 33950 125BC.040 1608cc

1973 124CS 59592 125BC.040 1608cc

1973 124CS 63308 132AC.040.3 1592cc

1974 124CS1 71650 132A1.040.4 1756cc

FIAT 124 Spider

1975 124CS1 88792 132A1.040.5 1756cc

1975 124CS1 132A1.031.5 1756cc

1976 124CS1 99909 132A1.040.5 1756cc

1976 124CS1 132A1.031.5 1756cc

1977 124CS1 113343 132A1.040.5 1756cc

1978 124CS1 132A1.031.5 1756cc

1978 124CS1 126001 132A1.040.5 1756cc

1978 124CS1 132A1.031.5 1756cc

1979 124CS2 142514 132C2.040 1995cc

1980 124CS2 132C2.031 1995cc

1980 124CS2 157654 132C3.040 1995cc

1981 – 1985* 124CS0 171001 132C3.031 1995cc

* Pininfarina Sold the 124 as the “Azzura” and “Spidereuropa” after 1982

10

Engine Maintenance + Modification

FIAT 124 Spider

4. Carburetion

FIAT Spiders manufactured from 1967 through 1980 were equipped with carburetors,
except in California where the 1980 model year introduced fuel injection. Carburetors
were provided by Weber SpA (Italy). FIAT and Weber have a long history; in the 1920s
Eduardo Weber began producing carburetors for conversion kits intended for FIAT
vehicles. His designs were the first progressive twin-barrel types with one barrel smaller
than the other. Various updraft, downdraft, and sidedraft designs were produced by
Weber and the carburetors were installed on vehicles ranging from small engine street
cars to twelve cylinder racing cars. Weber carburetors are still used today in off-road,
racing, and street applications.

4.1 Understanding Carburetors

An easy way to understand how a carburetor works is to study a very simple type, the
single-barrel, updraft carburetor. After this brief introduction we’ll work through
subsequent improvements to arrive at carburetors similar to the one on your FIAT.

F

A

B

E

D

C

Figure 2: Updraft Carburetor. A Float Chamber Vent , B Fuel Bowl or Chamber, with Float , C Spray Tube,

D Fuel Jet , E Venturi , F Throttle

Referring to figure 2, an updraft carburetor has the following features:

• A fuel bowl or chamber (A) in which a float-controlled needle valve keeps the

fuel constantly at a level 5-6mm lower than the fuel in jet (D).

11

Engine Maintenance + Modification

FIAT 124 Spider

• A Venturi (E). The purpose of the venturi is to increase the depression acting on

jet (D) to favor the vaporization of the gasoline sprayed from the jet during
engine operation.

• A spray tube or nozzle (C) through which fuel flows from float chamber to

calibrated jet (D).

• A throttle (F) that regulates the amount of fuel/air mixture drawn in by the

engine.

Updraft carburetors were understandably impractical. Carburetors quickly progressed to
down draft types, with an important improvement known as air bleed correction.

4.2 Air Bleed Correction

Emulsion tubes mixed air with the fuel prior before entering the carburetor. This air
bleed correction (figure 3) made operation more efficient.

Figure 3: Air Bleed Correction. A Float Chamber Vent , B Fuel Bowl or Chamber, with Float , C Spray

Tube, D Fuel Jet , E Venturi , F Throttle , G Air bleed jet, H Well for emulsion tube, I Emulsion Tube

A perforated emulsion tube (I) enables air and fuel to be mixed prior to being sprayed
into the carburetor barrel. This results in fuel “misting” into the barrel. The arrangement
allows for larger jets and supply tubes and a wider range of tuning. Air enters the
emulsion tube through an air bleed correction jet. The jet is removable, allowing for
precise adjustment of how much air is allowed into the emulsion tube well. There is one
well, emulsion tube, and jet per carburetor barrel.

12

Engine Maintenance + Modification

FIAT 124 Spider

4.3 Idle Speed Control

An additional improvement is an idle speed device (figure 4). This device allows your
engine to maintain the lowest rpm rate at which it will keep running.

Da

T

Db

D

4

2

Figure 4: Idle Speed Circuit. D main fuel jet, Da idle speed air jet, Db idle speed fuel jet, 1 idle speed

mixture orifice, 2 transition device, 3 idle speed mixture adjusting screw, 4 throttle setting or idle speed

1

3

adjusting screw

The throttle is nearly closed and fuel is drawn from below the throttle plate, rather than
from the main jetting. The idle speed device is an independent circuit on the carburetor,
sharing the fuel bowl with the main circuit but having its own mixture setting, jetting,
and an idle speed screw to regulate throttle position and engine speed.

4.4 Transition

We’ve reviewed the main and idle stages of a carburetor, so let’s take a look at how your
carburetor transitions smoothly from the idle stage to the main stage. In the side of your
carburetor barrel are holes, known as progression holes or transition orifices. Movement
of the throttle past these holes draws fuel into the engine (specifically, a drop in pressure
draws fuel through the holes as the throttle passes), creating additional speed while
building up to the main stage.

13

Engine Maintenance + Modification

FIAT 124 Spider

Idle Transition

Main

C

E

2

D

Figure 5: Transition Stage. 1 idle mixture orifice, 2 transition orifice, C spray nozzle, E venturi, F throttle

1

As the throttle continues to move the idle circuit, fuel feed to the progression holes will
cut off, and the engine will run entirely on the main circuit. Figure 5 depicts a carburetor
with a single transition orifice; in reality your carburetor may have several to make a
smooth transition. Without these holes the engine would stutter between the idle and
main stages.

Holes in the side of the carburetor are not enough to keep the transition and power
curves smooth. Your FIAT Spider has a “quick throttle,” meaning that throttle
movements can be fast enough to cause a lean condition. To compensate for this your
carburetor is fitted with an accelerator pump, used to inject additional fuel during the
transition stage.

4.5 Acceleration Pump

FIATs use a diaphragm-type accelerating pump, as depicted in figure 6. A roller under
the throttle mechanicals rests on a plate. When the throttle is moved the plate turns
against the roller, causing an arm to press the diaphragm in and force fuel through the
pump jet and into the stream of air passing through the carburetor. This richens the
mixture of fuel to compensate for the lean condition caused during quick throttle
movement.

14

Engine Maintenance + Modification

FIAT 124 Spider

L

K

J

N

2

3

M

F

4

5

Figure 6: Diaphragm-type accelerating pump – 1 Control lever, 2 Pump spring, 3 diaphragm return spring,

4 Cam lever, 5 Roller, F Throttle, J inlet valve, K Delivery valve, L Pump jet, M pump drain jet, N Pump

diaphragm

1

4.6 Cold Starting

On a cold morning your FIAT may be hard to start. If things are working properly you will
do one of three things to set the cold start device. You may pull a knob under your
dashboard. This knob is connected to a cable that moves a metal plate over the top of
your carburetor. If you have a later model FIAT (specifically those fitted with the ADHA
or ADFA carburetor) you might press the accelerator to the floor before starting the car
and then release it. This sets a semi-automatic, water-controlled mechanism in place.
This mechanism moves a metal plate over the top of your carburetor as well. Finally,
you might do nothing, meaning that you have an electric choke on a non-standard
carburetor. In case you’re wondering the electric choke also moves a metal plate over
the top of the carburetor. In all types this metal plate “chokes” the carburetor,
restricting the amount of air entering the engine but having no effect on the amount of
fuel. This causes a very rich condition, conducive to cold starting.

In figure 7 a simple choke is depicted. A plate moves upward, restricting airflow into the
barrel but not fuel. Once engine operating temperature is reached the choke is disabled
and normal airflow returns. Improvements in chokes over the years made them more
convenient and efficient. An automatic choke will vary the position of the restricting
plate as engine temperature increases, until the choke plate is fully open at normal
operating temperature. Weber refers to this as an “anti-flooding device” as flooding an
engine will occur if a choke is left fully “on” during normal temperatures.

15

Engine Maintenance + Modification

FIAT 124 Spider

O

P

C

E

F

Engaged Disengaged

Figure 7: Offset choke, P choke valve, C spray nozzle, E venturi, F throttle, O calibrated spring

4.7 Multi-Barrel Synchronization

We now move into the final discussion on carburetor operation, the multi-barrel
carburetor. Multi-barrel - in our case dual barrel - carburetors were designed to solve
several problems. Efficient fuel delivery into a four cylinder engine is difficult with one
single barrel carburetor. Fitting multiple single barrel carburetors, such as one per
cylinder or one per two cylinders would achieve good efficiency but introduce complex
(and expensive) throttle assemblies, complicate the fuel line plumbing, etc.

A dual-barrel carburetor provides for sharing of common components, such as the fuel
bowl and throttle mechanicals. There is also a single idle circuit in a dual-barrel
carburetor, simplifying tuning and making low-speed operation (such as driving in city
streets) more efficient. Dual-barrel carburetors work through the synchronization of the
throttle plates in each barrel.

16

Engine Maintenance + Modification

FIAT 124 Spider

Figure 8: Mechanically controlled differential opening of the throttles. F1 Primary throttle, F2 Secondary

throttle, Q Accelerator level integral with primary throttle F1, R Intermediate lever for control of secondary

throttle F2

The synchronization is established through a mechanical or vacuum linkage that activates
the secondary barrel when the primary barrel is approximately 2/3 open.

In figure 8, our carburetor starts with the throttles at rest. A throttle arm (A) rotates the
primary throttle (F1), bringing the carburetor through idle and progression phases. An
intermediate lever (L) is activated at a mechanically set point, connecting the primary and
secondary (F2) throttles. As the main throttle reaches wide open throttle the secondary
is also fully open, with both barrels running on their main circuits.

A vacuum carburetor (figure 9) achieves the same goal in a different manner. Instead of
a lever in between the main and secondary throttles, a diaphragm is connected to the
secondary barrel. When a sufficient pressure drop is reached in the primary barrel the
secondary barrel begins to open. Progression of the secondary throttle is always
controlled by the pressure drop in the primary barrel, making the vacuum carburetor
somewhat less “snappy” than the mechanical type.

17

Engine Maintenance + Modification

FIAT 124 Spider

Figure 9: Vacuum controlled differential opening of the throttles – 1 Interconnection between primary

venturi E and diaphragm S, E Venturi, F1 Primary throttle, F2 Secondary throttle, S Diaphragm for
operation of secondary throttle F2, Q accelerator level integral with primary throttle F1 –R intermediate
level for control of secondary throttle F2 activated by the movement of diaphragm T integral to vacuum

operated spring mechanism S

4.8 Carburetor Identification and Schematics

Weber stamped an identification number on your carburetor body. Depending on the
construction of the carburetor body, this number may be between the middle and lower
halves of the carburetor, or on the lowest mounting flange on the “front” (facing the
fender) or “back” (facing the cylinder head) side. It may in a different location altogether
but should be fairly easy to spot. The number may be quite long, but the primary
information is in the first few positions. Figure 10 shows the base of a 1970 Weber
26/34 DHSA1.

18

Engine Maintenance + Modification

FIAT 124 Spider

Figure 10: DHSA1 Carburetor Base Plate

Weber nomenclature is not easy to decipher. The important thing to note is the
numbers before the letters and the letters themselves. If you read “26/34 DHSA 1 OC”
then you can simply note that you have a “26/34 DHSA”. The numbers following the
letters indicate things like barrel size, factory jetting, emissions control modifications,
etc. The variations are minor but almost impossible to track. Using the chart below,
note whether or not your carburetor was original equipment on your engine:

Table 2: Carburetor Identification

Vehicle Year Displacement Carburetor

124 Spider 66-67 1438 34 DFH

124 Spider 68-69 1438 26/34 DHSA1

124 Spider 70-71 1438 26/34 DHSA1

124 Sport Spider 71-73 1608 28/36 DHSA2 or 3

124 Sport Spider 71-73 1608 Dual 40 IDF

124 Sport Spider 73 1592 28/36 DHSA2 or 3

124 Spider 1756 74 1756 34 DMSA

124 Spider 1756 75-76 1756 32 ADFA

124 Spider 1756 77-78 1756 32 ADFA

Spider 2000 79-80 1995 28/32 ADHA

19

Engine Maintenance + Modification

FIAT 124 Spider

4.8.1 Weber DFH

The DFH was used on early production 1438cc Spiders. It is not a common item on cars
imported into the United States. The DFH is operationally similar to the DHSA carburetor
fitted on later models.

4.8.2 Weber DHSA

The DHSA was used on the 1438 and 1608 motors. Vehicles imported into the United
States received the 26/34 DHSA1 and the 28/36 DHSA2. The numbers refer to the
primary (26 or 28) and secondary (34 and 36) barrel sizes.

Figure 11: DHSA2 Carburetor

The DHSA is a progressive two-barrel carburetor with a vacuum operated secondary.
This secondary throttle opens when the primary throttle is fully open. This opening is
controlled by a diaphragm mounted on the side of the carburetor and linked to the
secondary throttle shaft (refer to figure 9 in the previous section). The different DHSA
models are directly interchangeable with each other and with the DMS and DMSA
carburetors.

The DHSA has a mechanically operated choke, meaning that a cable connects the choke
plate to a knob. The driver pulls the knob, activating the plate, and restricting airflow into
the carburetor.

There are two additional small diaphragms that are electrically activated by the position
of the clutch. These devices are also attached to fast idle speed controller, electronically
linked to the clutch assembly and to a switch on the transmission. When you shift into
or out of 3
The actual speed at which the controller engages is set by a switch in the engine
compartment.

rd

, 4th, and 5th gears the controller keeps the engine speed around 1500 RPM.

20

Engine Maintenance + Modification

FIAT 124 Spider

The diagrams on the following pages show the exploded views of the DHSA carburetor.
For a description of the operation of the carburetor refer to the section on the DMSA.
The DMSA is operationally similar with the exception of the vacuum secondary.

Figure 12: DHSA External Parts, Float Mechanisms, and Choke Assembly

Figure 13: DHSA Jetting, Throttle Mechanisms, and Internal Parts

21

Engine Maintenance + Modification

FIAT 124 Spider

4.8.3 Weber IDF

European 1608 Sport Spiders produced from 1971 until 1973 were fitted with dual
Weber 40 IDF carburetors. Although never an option for U.S. cars many of the manifolds
and carburetor pairs were installed on Spiders of virtually every engine displacement
from 1608 to 2000. Although no FIAT manifold directly fit the 1438 series, an Abarth
manifold was produced that would allow for IDFs on that engine.

The FIAT Abarth Spider CSA (1972), a rare factory produced street version of an Abarth
race car, was also fitted with dual IDFs. The actual racing version had dual 44 IDFs
carburetors or mechanical fuel injection.

Figure 14: IDF Carburetor Side View

Through needle valve (6) fuel passes into bowl (2) where float (3), hinged on pivot pin (1),
controls needle (5) stroke to keep the fuel level constant. Needle (5) is connected to the
lug of float (3) via return latch (4).

Figure 15: IDF Normal Operation

22

Engine Maintenance + Modification

FIAT 124 Spider

From bowl (2), through main jets (18), fuel reaches wells (17). After mixing with the air
from emulsion tubes (16) and air corrector jets (9), the fuel reaches the carburetion area
consisting of auxiliary venturis (11) and main venturis (12) via nozzle (10). The carburetors
incorporate a mixture enriching device whose principle of operation is as follows: Fuel is
drawn from bowl (2) through calibrated holes in tubes (8) and into the carburetor through
spray tubes (7) during high speed operation.

The illustration shows also the crankcase emission control system — diagrams A and B
—. The crankcase emission control system consists of a rotary blanking disc (22) driven
by spindle shaft (14) controlled by lever (13). Through slot (21) the blanking disc connects
blow-by gas tube (19) with the downstream side of butterfly valves (15). Even with
butterflies (15) in idling speed position gas suction is controlled by calibrated hole (20).

Figure 16: IDF Progression

From wells (17) fuel passes to idle jets (24) via ducts (25). Emulsified with the air coming
from calibrated bushes (23) through ducts (26) and bushes (28), adjustable by means of
screws (27), the mixture reaches carburetor ducts on downstream side of butterflies
(15).

Bushes (28) are calibrated to control idling speed output.

Starting from idle condition, when butterflies (15) are progressively opened the mixture
reaches the carburetor ducts via progression holes (32) to bring about an increase in
engine angular velocity. To obtain a consistent air feed in both carburetor ducts with
butterflies (15) in idle position, a variable volume of air from ducts (30), depending on the
position of screws (31), is fed to the downstream side of butterflies (15) through holes
(29) situated in alignment with adjusting screws (31).

23

Figure 17: IDF Acceleration

Engine Maintenance + Modification

FIAT 124 Spider

Upon closing butterflies (15) lever (37) frees diaphragm (41) which, under the pressure of
spring (40), draws fuel from bowl (2) through ball valve (38).

Upon opening butterflies (15) diaphragm (41) under the action of cam (36) and lever (37)
injects fuel into carburetor ducts through ways (35), delivery valves (33) and pump jet
nozzles (34). Spring (39) dampens any sudden butterfly opening and prolongs fuel
delivery.

The excess fuel delivered by the accelerating pump is exhausted into bowl (2) together
with the pump chamber vapours, through calibrated bush (42).

Figure 18: IDF Cold Start Devices

From bowl (2) fuel passes to the starting device through ducts (44) and starting jets (43).
Emulsified with the air from holes (50), fuel reaches the recess of valves (49) through
ducts (45) and holes (46). Then, completely emulsified with the air drawn from holes

24

Engine Maintenance + Modification

FIAT 124 Spider

(48), the mixture is conveyed to carburetor ducts on downstream side of butterflies (15)
via ducts (47).

Starting with a cold engine - Starting device ON - position A.

Starting with a semi-warm engine - Starting device partially ON - Position B.

Engine warm-up - During this stage, even with the vehicle in motion, disengage the
starting device gradually.

Normal operation - Starting device OFF - Position C to be restored as soon as the engine
reaches normal operating temperature.

Figure 19: IDF Dimensions

4.8.4 Weber DMSA

The DMSA was used for a single year (1974). It is virtually identical to a DHSA except it
lacks the vacuum operated secondary. DMSA has a mechanically-operated secondary
and the largest primary and secondary throttles of any carburetor installed on the
Spiders. The advantage over the DHSA is there is no time lag during heavy acceleration
for manifold pressure to pull open the secondary. The DMSA is a slightly larger
carburetor than the DHSA2; this was to accommodate for the larger 1756cc engine
introduced in 1974.

25

Engine Maintenance + Modification

FIAT 124 Spider

Figure 20: DMS Carburetor Side View

The DMSA and DMS are popular upgrades for DHSA owners. Problems with the
vacuum-operated secondary unit (typically stemming from a misunderstanding of how it
works) would lead to cars that ran poorly. The DMS, with a direct mechanical
connection between the throttle plates, eliminated these problems. As DHSA
carburetors wore out they were often replaced with brand new DMS units.

Figure 21: DMS Normal Operation

Through needle valve (1) fuel passes into bowl (17) where the float (18) hinged on pivot
pin (20) sets the needle (2) opening to keep level constant: the needle (2) is connected to
float tab (18) via return hook (19). From bowl (17) through main jets (16) fuel reaches
well (15). After mixing with the air from orifices of emulsion tubes (14) and air corrector
jets (5), through nozzles (9) fuel reaches the carburetion area consisting of auxiliary
venturis (10) and main venturis (11). This carburetor is provided with a mixture-enriching

26

Engine Maintenance + Modification

FIAT 124 Spider

device on the primary (34 DMS/201) or secondary barrel (34 DMS 1/201 - 34 DMS
2/201): from bowl (17) the fuel metered by a calibrated bush (3) get mixed with the air
coming from calibrated orifice (4).

The mixture thus formed through duct (6) and calibrated bush (7) is drawn via duct (8) ­into the carburetor primary or secondary barrel during high speed running.

The figure also shows the device for differentiated opening of throttle valves. Upon
actuating throttles control lever (25) the tab (26) of the lever plate (22) fixed on primary
shaft (12) turns and the primary throttle (13) opens by an equivalent angle whilst the
secondary throttle (24) on spindle (23) remains closed.

Subsequently, tab (26) contacts the lug (27) of idle lever (21) which, by shifting the lever
(28), rotates the secondary spindle (23) until both throttles are simultaneously wide open.

The figure above also shows the device for gases aspiration from engine crankcase ­schemes A and B. It consists of a rotary blanking disc (31) driven by primary shaft (12)
which through groove (32) connects the tube (29) - conveying gases to be aspirated ­with the area downstream of primary throttle (13). Even with throttles in idle position,
conveyance of aspirated gases still takes place and is metered by the calibrated orifice
(30).

Figure 22: DMS Progression

27

Engine Maintenance + Modification

FIAT 124 Spider

From emulsion tube (15) the fuel is drawn to idle jet (48) through duct (42): emulsified
with the air from calibrated bush (49) via duct (46) it get mixed with the air from
calibrated orifice (47) and reaches the carburetor primary barrel downstream of throttle
(13) through the calibrated bush (37) adjustable by screw (41).

Mixture reaches the primary barrel also from duct (45) through calibrated hole (44) where
it is further emulsified with the air entering from hole (43) and conveyed downstream of
throttle (13) via the hole (38) adjustable by screw (40) - (by-pass idling).

Starting from idle rate and gradually opening throttle (13) mixture flows to primary barrel
also from progression holes (39) thus allowing a smooth increase in engine angular
speed.

When opening the secondary throttle (24), the fuel coming from secondary emulsion
tube passes to idle jet (34) through the duct (35): emulsified with the air from calibrated
bush (33) via duct (36) it flows to secondary barrel through progression holes (50) placed
at throttle (24) level which allow a steady increase in engine angular speed.

Figure 23: DMS Acceleration

Upon closing throttles, the lever (58) frees diaphragm (57) which through action of the
spring (55) draws fuel from the bowl (17) through ball valve (54). Upon opening throttles
by means of cam (59) lever (60) and lever (58), the diaphragm (57) injects fuel in
carburetor primary barrel via duct (61), delivery valve (51) and pump jet (52). Spring (56)
absorbs quick opening of throttles and extends fuel delivery stage. Any excess fuel

28

Engine Maintenance + Modification

FIAT 124 Spider

delivered by the accelerator pump is exhausted into bowl (17) along with pump chamber
vapors, through the calibrated bush (53).

Figure 24: DMS Starting

With lever (63) in position A >, butterflies (62) blank the carburetor air intakes whilst
throttle (13) opens partially by mean of rod (67) and lever (68) fast idle.

Thus nozzle (10) delivers a rich mixture allowing prompt engine starting.

Once engine is started, the vacuum acting on butterflies (62) and the action of diaphragm
(66) open butterflies (62) partially against action of spring (64).

In these conditions the mixture, still rich, allows normal engine running.

Once engine has reached the rated temperature, disengage the device completely ­position B “: butterflies (62) are kept wide open by the lug (65) whilst primary throttle
(13) is brought to idle position. Engine starting - engage starting device by pulling knob
completely out - position A

Engine warm-up - during engine warm-up, even with vehicle running, disengage the
device progressively. Normal running - device off - position B as soon as engine operates
smoothly at rated temperature.

29

Engine Maintenance + Modification

FIAT 124 Spider

Figure 25: DMS Dimensions

4.8.5 Weber ADFA

The ADFA was introduced in the 1975 model year and used through the 1978 model
year. It has a mechanically-controlled secondary and a choke that is controlled by water
temperature. This choke is semi-automatic; to activate it the gas pedal is pressed to the
floor. If the engine is cold this will release a spring-loaded toothed wheel that holds the
choke in place. There is no other manual action required; as engine water temperature
increases the spring expands, acting upon the toothed wheel and closing the choke in
stages.

Figure 26: ADF Carburetor Side View

30

Engine Maintenance + Modification

FIAT 124 Spider

Figure 27: ADF Normal Operation

Through needle valve (1), fuel passes into bowl (16) where the float (17), hinged on pivot
pin (19) sets the opening of needle (20) in order to keep fuel level constant: the needle
(20) is connected to the lug of float (17) through the return hook (18). The fuel, from bowl
(16) reaches wells (14) through main jets (15). After mixing with the air coming from
orifices of emulsion tubes (13) end from air corrector jets (6), the fuel reaches, vie
nozzles (8), the carburetion area consisting of auxiliary venturis (7) end venturis (9).

The carburetor is provided with the enrichment circuit on second barrel: from bowl (16),
the fuel, through duct (10) end calibrated bush (2), blends with the air coming from
calibrated orifices (3). The mixture thus formed will be sucked — through duct (4) end
calibrated pipe (5) — by the second barrel during full power operation at high r.p.m.

Fig. 1 also shows the device for differentiated opening of throttle valve. Acting on
throttles control lever (25), this will first travel a given idle distance: primary throttle (23)
— fitted on spindle (24) — will open of a corresponding angle, while secondary throttle
(12) — fitted on spindle (11) — remains in closed position. Successively, lever (25)
contacts free lever (22), which by shifting lever (21) makes the secondary spindle (11)
rotate until contemporary end complete opening of both throttles is reached.

Also shown in Fig. I is the control system for crankcase emission — diagrams A and B.
— This consists of a rotary blanking disc (29) driven by shaft (24) controlled by lever (25)
which, by means of groove (26) — diagrams A and B — connects pipe (28) conveying
gases to be sucked, with the area downstream of throttle (23).

Even by throttle (23) in idle position — diagram A — goes on conveyance of sucked
gases metered by calibrated orifice (27).

31

Engine Maintenance + Modification

FIAT 124 Spider

Figure 28: ADF Idle Speed and Progression

From primary well (30) fuel reaches idle jet (34) through duct (43): after emulsifying with
the air coming from calibrated bush (35), it flows through duct (42), calibrated bush (40)
— adjustable by screw (41) — and reaches the primary throat downstream of throttle
(23). The mixture reaches the primary duct also through progression holes (44) near the
primary throttle; this allows a smooth increase in engine angular velocity starting from
idle running.

By opening of secondary throttle (12), the fuel coming from the secondary well flows to
idle jet (36) through duct (38); after emulsifying with the air coming from calibrated bush
(37), it reaches, via duct (39), the secondary throat through progression holes (45).

Figure 29: ADF Acceleration

32

Engine Maintenance + Modification

FIAT 124 Spider

Upon opening of throttles, the diaphragm (50), under the action of cam (53) and lever
(52), injects fuel into primary carburetor throat through duct (54), delivery valve (55) and
nozzle (46).

Spring (51) absorbs quick throttle opening and allows regular feeding from jet (46). Any
excess fuel delivered by accelerating pump, together with pump chamber vapors, is
exhausted into bowl (16) through calibrated orifice (48). Upon closing throttles, lever (52)
sets free the diaphragm (50) which draws in fuel from bowl (16) through ball valve (47),
under the action of spring (49).

Figure 30: ADF Starting

The choke is of semi-automatic type: this means that to insert it when engine is cold, it
is necessary to depress the accelerator pedal completely, then to release it slowly to
normal position.

Once the starting device is inserted, the bimetallic coil (68) — via lever (67), spindle (56),
lever (57) and rod (58) — keeps the choke plate (59) closed. At the same time, the cam
lever (60) will be in the position as shown in Fig. 4 and, by means of lever (25) —
adjustable by screw (61) — it will keep the primary throttle (23) partially open (fast idling).

In these conditions, the nozzle (8) delivers a given amount of mixture which, diluted with
the air controlled by starter plate gape, allows a quick starting of the engine.

After starting, the vacuum set up beneath throttle (23) through duct (64), acts on
diaphragm (65) which being displaced by rod (66) and bush (62) the latter held by the
spring (62) make the lever (67) rotate against the action as the bimetallic coil (68) which,
via spindle (56), lever (57) end rod (58), will partially open the starter plate (59) thus
supplying a mixture strength suitable to allow a normal engine running.

33

Engine Maintenance + Modification

FIAT 124 Spider

Should the accelerator be depressed when the choke is included, the screw (61) would
disengage the cam (60) which drawn by spring (63) would reduce the opening of primary
throttle (23).

The engine cooling-water warms up, and, circulating in the cover (70) heats the bimetallic
coil (58) which will make the lever (67) turn and through the above mentioned linkage
system, will cause the progressive opening of choke plate (59). During rotation of
primary throttle (23), the cam lever (60) will also rotate thus excluding progressively the
choke.

Once running temperature is reached, the choke plate (59) will be in fully open position:
the screw (61) is now no longer in contact with the cam (60) thus allowing primary
throttle (23) to close up till to normal idling position.

Figure 31: ADF Anti-Pollution Device

ADF type carburetors, provided with vacuum devices to reduce air pollution, are fitted on
cars equipped with electric switches that set off a special electro valve located between
intake manifold and fuel inlet pipe (74).

The vacuum, through pipe (74), acts on diaphragm (73) which, by means of rod (72),
lever (71) and lever (53), opens primary throttle (23) to fast idle position: adjustment of
throttle (23) opening is carried out through adjusting screw (75).

Under such opening conditions, during motoring over, exhaust emission levels are rather
low; within the air pollution tolerances. When vacuum is intercepted by the electro valve,
the air sucked through duct (76), nullifies vacuum acting on diaphragm (73) and allows
throttle (23) to return to normal idling position.

34

4.8.6 Weber ADHA

Figure 32: ADF Dimensions

Engine Maintenance + Modification

FIAT 124 Spider

The ADHA is similar to the ADFA except for the secondary barrel, which is vacuum
controlled. This is a hard carburetor to love. Introduced with the 2000cc engine the
ADHA was a small carburetor on the largest of the Spider motors. Although a carburetor
with 23mm and 32mm barrels should be adequate for a 2 liter motor, the jetting, intake
manifold, and array of pollution control devices both on and off of the carburetor resulted
in a fairly uninspiring driving experience.

4.9 Carburetor Tuning

These are the recommended procedures per Weber with some modifications, you will
find the same general steps in any publication on setting up carburetors. Should the
engine fan come on during these steps STOP working (leave the engine running) until it
shuts off. Fans draw current from the alternator, creating a load that will reduce engine
speed and may cause you to make incorrect adjustments. Fans are also dangerous to
work around.

4.9.1 Set Carburetor to Factory Settings

Back out the idle speed screw until it is no longer in contact with the throttle stop lever.
Now turn the screw until it contacts the lever and again 1 ½ turns.

Turn the idle mixture screw (on our carburetors it is typically in the center bottom of the
carburetor body) in until it is fully seated - do not force the screw. Now turn it back out
two full turns.

4.9.2 Start and warm the Engine

Disengage or block the choke open. On automatic chokes you can use a small clamp or
wire to pull the choke mechanism open. The engine should start and run poorly (if it

35

Engine Maintenance + Modification

FIAT 124 Spider

does not remain running then increase the idle speed screw ½ turn until it does). Adjust
the idle speed screw until the engine runs at approximately 900 RPM.

Let the engine warm up to operational temperature. On a Spider you will typically wait
until the fan has cycled two times (on-off-on-off). Turn the mixture screw in (lean the
mixture). If the engine increases in speed then continue to turn until it is no longer
increasing or runs worse, then back the screw out ½ turn. If the engine decreases in
speed then turn the screw out until it is increasing in speed. Continue to turn until it is
no longer increasing or runs worse, then turn the screw in ½ turn. Adjust the idle to
approximately 850 RPM.

4.9.3 Final Settings

Set the idle speed screw so that the engine runs at 850 RPM, or 900 RPM if you have air
conditioning. Recheck the mixture screw by turning slightly in then out. Engine speed
should be set - using the mixture screw ONLY - to the fastest and smoothest point of
operation (listen for exhaust popping). Reset the idle speed screw as necessary.

Drive the car under various loads (idle, cruise, hard acceleration, gradual acceleration,
etc.) for a short period of time then remove one of the spark plugs. The electrode should
be brownish-white in color. A white plug results from an engine that is too lean; a black
plug from one that is too rich. Adjust the mixture screw slightly to compensate.

4.10 Diagnostics and Troubleshooting

4.10.1 Air Input Diagnostics

The only source of air entering the engine should be through the carburetor barrels. Air
entering the engine through a broken gasket or carburetor spacer can cause poor
running. You can spray carburetor cleaner around the base of the carburetor; there
should be no change in engine speed. Also check the tightness of the bolts holding the
carburetor to the manifold, they should be tight (but not so tight you’re bending the base
plate!).

If you find that air is entering around the throttle assembly then you might have throttle
rods and bushings that have worn themselves out. The carburetor will need to be rebuilt
or replaced. Also inspect the carburetor body for any cracks or leaking fuel. Cracks can
let in air and typically require the carburetor to be replaced.

4.10.2 Mixture Problems

If problems appear to be stemming from the fuel mixture there are a few areas to
diagnose, all of which deal with the basic air/fuel mixture settings on the carburetor.

Always too lean

If the vehicle runs too lean, even with the mixture screw “all the way out” (meaning to
the limit of reasonable travel, or about 4-5 turns) then you may have idling jets that are

36

Engine Maintenance + Modification

FIAT 124 Spider

too small. Consider increasing the idle jet size by adding 10 to the size (if you had a 45,
increase to 55) then re-set the mixture. Continue up (or down) in increments of 5 or 10 if
this appears to be helping.

Always too rich or very limited adjustment range

If the vehicle runs too rich, even with the mixture screw “all the way in” (seated) then
you may have idling jets that are too large. Consider decreasing the idle jet size by
subtracting 10 from the size (if you had a 55, increase to 45) then re-set the mixture.
Continue down (or up) in increments of 5 or 10 if this appears to be helping. Also apply
this procedure if your mixture is correct by barely moving the mixture screw open as this
will limit your ability to tune the mixture.

Idles with mixture screw seated

If your carburetor idles with the mixture screw fully seated then the car is idling on the
main throttle and not on the idle jets. Reset your throttle linkage by using the procedure
described in the tune-up section. If this fails to solve the problem then observe your
carburetor spraying fuel during operation and look for leaks. The accelerator pump may
be leaking into the main barrel during idle operation, causing enough fuel to mix (and mix
poorly) to maintain idle.

Poor transition / flat spots in acceleration

During acceleration the transition between the idle, progression, and wide-open stages
should be smooth. If not then your secondary idle jet, main jet, or secondary jet may be
too small, causing a lean condition in between stages. If you are running a stock
carburetor on a reasonably stock engine then check that the jets meet or in the same
basic range as was stock for your model year.

Puffing and mild backfires

The mixture can cause puffing and mild backfires at or outside of the idle stage. If you
are having these issues then open the mixture screw 1/8 turn and note any change. This
will slightly richen the mixture and may eliminate these lean conditions. Continue in 1/8
increments until you’ve reached a full turn, if there is no difference then reset and check
the timing, adjusting as necessary.

37

Engine Maintenance + Modification

FIAT 124 Spider

5. Fuel Injection

FIAT Spiders manufactured from 1967 through 1978 were equipped with carburetors.
Vehicles manufactured from the 1980 model year through the end of production in 1985
were equipped with electronic fuel injection. There is some argument about the
transition from carburetion to fuel injection. The most plausible story is that FIAT first
offered fuel injection as an option, then as standard equipment in California, then as
standard equipment for the entire line. Regardless of when or why you can always tell
what system your vehicle had installed by looking at the body style number. This is the
first four or five positions in your vehicle’s VIN number. The VIN is stamped in your
engine compartment, on a small metal plate on your dashboard (near the driver’s side
windshield), and on some models inside the driver’s side door. The first three positions
will read “124” or (on later vehicles) “ZFA124”, followed by a two letter “primary” body
code.

AS, BS, CS1, CS2: Carburetion

CS0, DS: Fuel Injection

VX: Carburetion / Supercharger

Fuel injection systems were provided by Bosch GmbH (“Bosch”). Carburetion and fuel
injection approach mixing fuel and air in very different ways. Simply put, a carburetor
mixes fuel outside of the combustion chamber. The mixture is drawn through a plenum
into the combustion chamber. In a carburetor the settings that govern the mixture of
fuel and air remain relatively static, fixed mechanically by the jets and orifices in the
carburetor and when the vehicle is tuned. A fuel injection system sprays metered fuel
directly into the manifold at the intake port during the intake cycle. The Bosch system
used in a FIAT electronically controls the amount of fuel, resulting in more dynamic
control of air to fuel ratios.

By the end of the 1970’s fuel injection systems were slowly overtaking carburetion on
the drawing boards of automotive engineers. Driven by emissions control regulations
and a noticeable improvement in performance and fuel economy, fuel injection was
evolving from complex mechanical systems to electronic “engine management”
systems. The Bosch L-Jetronic system was used on the majority of European fuel
injected cars, including FIAT, Alfa Romeo, Ferrari, Lamborghini, Lancia, BMW, Mercedes,
Porsche, Renault, Volkswagen, and Peugeot. It was preceded by a number of
mechanical systems, including the K-Jetronic by Bosch and mechanical systems by

38

Engine Maintenance + Modification

FIAT 124 Spider

SPICA, Kugelfischer, and others. Unlike its predecessors, L-Jetronic had an electronic
brain controlling the injector pulse and numerous sensors telling the brain what the fuel
system was doing. It is superseded by Bosch Motronic. Unlike Motronic, L-Jetronic is
not as tightly integrated with the engine; one could consider L-Jetronic a “bolt-on” fuel
injection system where Motronic is more “engineered in” to the engine design.

Bosch has always been a leader in fuel injection worldwide because of its association
with Mercedes and their leadership with diesel and aircraft engine design. Bosch began
developing electronic fuel injection in the 1950s and licensed some early American
designs as well. Bosch introduced electronic control to its production fuel injection
designs in 1974. A more sophisticated and reliable system, the L-Jetronic soon
emerged. An oxygen sensor followed and was quickly adopted by European car makers
including FIAT who were struggling to make small high performance engines meet the
1980 California and 1981 U.S. Federal emissions requirements.

5.1 Fuel injection Basics

Figure 33: Bosch L-Jetronic Fuel Injection as used in the FIAT Spider 2000.

39

Engine Maintenance + Modification

FIAT 124 Spider

The FIAT implementation of the Bosch L-Jetronic fuel injection system is relatively
simple and uses the most basic components required to operate the system. Many
additional options including atmospheric pressure sensors, knock sensors, and crank
angle sensors, are all possibilities with L-Jetronic but were never installed. FIAT quite
literally built a system around the existing 2000cc carbureted engine. The simplicity
results in a system that is inexpensive, easy to diagnose, and can be repaired by the
home mechanic. The system consists of a number of components that are located in
the engine and passenger compartments. Figure 33 summarizes the major components
and some of their connections.

5.2 The Air Flow Meter and Fuel Pump

The air flow meter is positioned just above the air filter and is the only point of entry for
air into the fuel injection system. Inside is a spring-tensioned flap connected to a
rheostat. As intake air volume increases the flap moves an arm against the rheostat.
The rheostat converts the movement of the flap into an electrical current that is sent to
the fuel injection computer and is the primary input in the system. Fuel is delivered in
proportion to the volume of air and the fuel injection computer adjusts the fuel delivery
to best find the 14.7:1 air to fuel ratio.

The stream of new air passes through the main air hose (also called the “big air hose”),
connecting to the throttle body. The operation is abbreviated as follows:

1. Air passes the throttle plate into the plenum (the square aluminum box on the
engine intake side) and is drawn through runners (pipes under the plenum) into
the engine.

2. The fuel injection computer opens the injectors and sprays fuel into the intake
runners (the four tubes between the plenum and the cylinder head). All four
injectors fire at the same time.

3. Valves open and draw the mixture into the combustion chamber.

4. The mixture is compressed and explodes via ignition spark.

5. The mixture is expelled.

6. An oxygen sensor measures the amount of unburned oxygen in the exhaust.

7. The F.I. computer uses the reading from the oxygen sensor to adjust the next
mixture.

40

Engine Maintenance + Modification

FIAT 124 Spider

The air flow meter also activates the fuel pump. Unlike the 3-5psi pumps of carbureted
engines, fuel injection pumps must produce the high pressure that forces fuel into a mist
while passing through the injector bodies. The pump fitted to the FIAT 2000 engine
produces between 50 and 80psi, which is controlled to between 36 and 43psi by the fuel
pressure regulator. As air passes through the air flow meter a chrome rod closes a
circuit that activates the fuel pump. So long as air is passing through the meter the
pump will run; once the vehicle stops drawing air the pump will shut off.

5.3 Cold Starting Components

Let’s discuss the fuel injection components that are used during cold-starting of an
engine. When a cold engine is started it requires substantially more fuel than a warm
engine. This is due to condensation of the fuel in the air/fuel mixture. A device called a
thermo-time switch (see Figure 34) is located directly under the Spider intake manifold.
This switch determines the length of time the cold start valve, remains on. The cold
start valve is a fifth injector, inserted into the side of the plenum. This injector sprays
fuel directly into the air entering the plenum. This rich mixture remains until the engine
reaches a temperature sufficient to eliminate condensation of fuel and keep the engine
running. This process takes from 2 to 8 seconds depending on the coolant temperature.

Figure 34: Cold Start Operation in the Bosch L-Jetronic System

41

Engine Maintenance + Modification

FIAT 124 Spider

5.4 Warm-Up Components

The warm up phase starts when the thermo-time switch heats up and closes the cold
start injector. The engine temperature sensor, located in the water coolant “T” in front
of the cylinder head, sends coolant temperature readings to the fuel injection computer.
The engine is still cool enough to have increased frictional resistance and, without
additional fuel and an increased idle speed, will stop running. To compensate the fuel
injection computer turns on a device called an auxiliary air regulator. This device allows
air to be drawn directly into the plenum, bypassing the throttle plate. The effect is an
increase in idle speed – the computer will give the engine more fuel to create an
appropriate ratio to the inbound air. Once engine temperatures reach the normal
operating range the auxiliary air valve closes. The engine now enters a “normal”
operating phase, with no cold or warm up devices operating.

Figure 35: Warm-up Operation in the Bosch L-Jetronic System

5.5 Idle Speed Control Components

Your FIAT fuel injection system maintains idle by allowing a small amount of air to
bypass the throttle plate and enter the throttle body. This amount of air is controlled in
three ways. First, the mixture is statically controlled by turning a bypass screw on the air
flow meter body. Next, the air strikes the throttle plate, which at rest is open
approximately 1 degree and allows a small amount of air into the plenum. Additional

42

Engine Maintenance + Modification

FIAT 124 Spider

airflow is directed through a passageway above the throttle and controlled by a needle
valve. In this way a fixed amount of air is allowed into the engine at idle, and that
volume of air is easy to adjust and control. This operation is depicted in Figure 36.

Figure 36: Idle Speed Control in the Bosch L-Jetronic System

5.6 Cruising, Accelerating, and Deceleration Modes

Normal driving conditions are typified by acceleration, cruising, full load, and
deceleration. During acceleration additional fuel is injected into the engine. This amount
of fuel is governed by the amount of air entering the air flow sensor. Heavy acceleration
(wide open throttle) results in a somewhat rich mixture while deceleration results in the
fuel injectors being shut off. During cruising the fuel injection computer calculates fuel
delivery so that consumption is low. The fuel injection computer keeps the mixture at
the leanest point of efficient operation. During each of these phases air temperature is
measured by a sensor in the air flow meter. Because air temperature has an effect on
the amount of fuel required to maintain good operation, the fuel injection computer will
use this input to alter the amount of fuel.

Fuel mixture management is based on optimum masses (weights) of the air/fuel
combination. It is not a measure of volume. L-Jetronic systems use the air flow meter
to estimate the air mass entering the system by measure air pressure and temperature.
During acceleration the air pressure against the air flow meter flap increases, signaling

43

Engine Maintenance + Modification

FIAT 124 Spider

the computer to increase the amount of fuel. The system will also increase or decrease
the amount of fuel based on the temperature of the air entering the system.

5.7 The Oxygen Sensor

A final sensor performs continuous monitoring of the exhaust gases. This input is used
by the computer to adjust fuel flow to best reach lambda. The oxygen sensor, also
known as a lambda sensor, is a ceramic and platinum electrode. The ceramic permits
diffusion of the oxygen present in the air. At engine operating temperatures it becomes
conductive; when the level of oxygen on one side of the electrode is different from that
on the other side a voltage is generated. This voltage is reported back to the fuel
injection computer. Sensor operation becomes effective at temperatures above 350
degrees Celsius; below this range the fuel injection computer receives no meaningful
input. Many vehicles employ heated oxygen sensors that output data to the computer
much faster; the FIAT uses the unheated type.

5.8 Other Components

If you flip back to the overview diagram (figure 33) you’ll notice a number of other fuel
injection pieces and parts that we did not cover. Some of them, such as the air
conditioner bypass valve, exist to provide extra air into the plenum when a load (such as
the a/c compressor) is switched on. Rarely do FIAT Spiders even have this valve, but if
you have the aftermarket air conditioner it may be fitted. You’ll also notice the fuel
delivery components, the fuel pump, fuel filter, fuel manifold, and fuel pressure
regulator. These are responsible for fuel delivery (pump), filtering (filter), routing
(manifold) and maintaining constant flow rates to each injector (regulator). The regulator
keeps the flow constant by increasing fuel pressure and manifold pressure is near
ambient and dropping pressure as the manifold vacuum increases.

44

Engine Maintenance + Modification

FIAT 124 Spider

5.9 Component Reference

The following pages contain sketches and part numbers for the various fuel injection
system components and brief descriptions of each.

Table 3: Major Fuel Injection System Components

Component Description

Lambda Sensor

P/N 0 258 001 051

The lambda sensor meters the presence of oxygen in the exhaust gases and
reports the level of oxygen to the ECU. It is located in the exhaust system
before the catalytic convertor.

Failure of this sensor will occur at approximately 30,000 miles or sooner on a
poorly operating engine and will result in reduced efficiency. An engine that
burns oil will ruin the sensor regularly.

Replace with good picture

Air Flow Meter

P/N 0 280 202 023

The air flow sensor is the point of entry for air into the fuel injection system. It
measures the volume and temperature of air entering the engine and switches
the fuel pump on when air is drawn into the engine.

Coolant Sensor

P/N 0 280 130 023

The water temperature sensor is a hex-head brass component located in the
cooling system pipes. On a 2000cc engine it is located in the coolant "T" in front
of the head and between the cam drive wheels and the radiator.

45

Component Description

Auxiliary Air Regulator

P/N 0 280 140 120 or 0 280 141 013 (Spider with A/C)

This device allows air to be drawn directly into the plenum, bypassing the
throttle plate. The effect is an increase in idle speed – the computer will give
the engine more fuel to create an appropriate ratio to the inbound air. Once
engine temperatures reach the normal operating range the auxiliary air valve
closes.

Fuel Pressure Regulator

Engine Maintenance + Modification

FIAT 124 Spider

P/N 0 280 160 214

The fuel pressure regulator receives fuel from the fuel pump and keeps the fuel
pressure into the injectors constant. It is located on the fuel rail and connects
(via the rail) to the injectors and fuel pump. A smaller vacuum hose connects
this regulator to the intake manifold. It maintains a constant flow rate at the
injector tip as manifold pressure varies; increasing fuel pressure when manifold
is near ambient and dropping it as the manifold vacuum increases.

Failure of this device can cause fuel starvation or too much fuel in the system,
affecting performance.

Fuel Pump

P/N 0 580 464 019

Located under the car and near the fuel tank, the fuel pump delivers fuel through
the fuel filter and the fuel rail and into the injectors.

46

Component Description

Fuel Injector & Seals

Fuel Li ne

P/N 0 280 150 127 (DS0 Spiders) or 0 280 150 121 (CS0 Spiders)

Engine Maintenance + Modification

FIAT 124 Spider

Connector

Body

Tip

Seals P/N 1 280 206 702 and 703

A fuel injector is an extremely simple electrical device. The ECU will send a
small current to the injector (via the connector), opening the injector and
allowing fuel from the fuel rail to spray through the tip and into the engine. The
tip of the injector is an insulator; the injector itself is a small opening in the
center of the tip. Injectors are seated in the manifold with large rubber isolators
around the tip and the injector body, insulating the injector from vibration.

Cold Start Injector

P/N 0 280 170 041

Upon receiving the "on" signal from the ECU, the cold start injector sprays fuel
into the intake plenum, creating the rich fuel mixture required during cold starts.
The duration of time in which the injector operates is determined by the thermo­time switch.

Double Relay

P/N 0 332 514 127

The double relay consists of two relays molded into a single container. It is
located near the ECU. Signals from the ECU enter the relay and trigger higher
voltage components.

47

Component Description

ECU

P/N CU97X

The ECU is a small computer located under the glove box. It is not a serviceable
component. The connector on the ECU is used to test many of the sensors in the
FI system.

Engine Maintenance + Modification

FIAT 124 Spider

5.10 Fuel Injection Tuning

A fuel injected Spider does not require (or allow) mixture adjustment. Tune-ups typically
include the steps outlined above (in “All Engines”), setting the idle speed, and adjusting
the throttle position switch. The oxygen sensor should also be replaced if it is old or
questionable.

5.10.1 Replacing the Oxygen Sensor

How old is your oxygen sensor? Don't know? Replace it. Sensors are good for
approximately 30,000 miles. However, if your engine is running very poorly then do not
replace the unit until good performance has been restored. No matter what you’ve read
or heard the oxygen sensor on your Spider is not going to cause the vehicle to run
poorly. Most people are not aware when the O2 sensor fails because the changes in
performance are typically minor. Certainly the engine runs better if all sensors are
working properly, but the O2 sensor will not cause your car to go from running great to
hardly running. If you’re having performance issues that are major look elsewhere and
leave your old O2 sensor installed so you don’t ruin a new one (they damage very easily
with overly rich or lean engines).

5.10.2 Idle Speed Setting.

Run the engine to normal operating temperature. On cars with automatic transmissions,
set the parking brake, block the wheels, and put the transmission in "D". Completely
seat the idle speed screw. Loosen the accelerator linkage stop screw retaining nut and
adjust the stop screw to achieve 800 to 900 RPM on manual transmissions and 700 to
800 RPM on automatic transmissions.

48

Engine Maintenance + Modification

Figure 37: Idle speed controls on the Spider 2000

FIAT 124 Spider

Lock the accelerator stop screw with the retaining nut. Use the idle speed screw (1) to
set idle at 850 to 900 RPM on manual transmissions and 700 to 800 RPM on automatic
transmissions. If idle speed cannot be reached using this procedure, fully remove the
idle speed screw (2) and clean the orifice and the screw itself using a high pressure
spray cleaner (carburetor cleaner is fine).

5.10.3 Throttle Position Sensor Adjustment

The throttle position sensor tells the ECU to turn off the injectors during deceleration.
Improperly set it can affect the travel of the throttle plates and cause poor transition from
full speed to cruise and idle operation.

Unplug the throttle plate switch. Note the connector blades (on the plate switch, not the
connector itself) are marked “3” “18” and ‘2”. Connect an ohmmeter between
terminals 2 and 18 of the switch. Loosen the two screws holding the switch in place.
Rotate the switch clockwise until the ohmmeter indicates a closed circuit. Tighten the
two screws and reconnect the switch.

49

Engine Maintenance + Modification

FIAT 124 Spider

5.11 Fuel Injection System Electrical Diagrams

These diagrams are part of a complete set for the 1980 – 1982 Spider available at

www.artigue.com/fiat

.

Figure 38: Primary Connections on the Electronic Control Unit

If you need a high quality print, download the diagrams from the website noted above
and print from that file to virtually any size. Most copy and print shops have large scale
plotters that can print on engineering size paper, such as 24 x 36 inches.

50

Engine Maintenance + Modification

FIAT 124 Spider

Figure 39: Primary Fuel Injection Circuits

51

Engine Maintenance + Modification

FIAT 124 Spider

Figure 40: Fuel Injection System Electrical Diagram

52

Engine Maintenance + Modification

5.12 Fuel Injection System Part Numbers

Table 4: Fuel Injection System Part Number Reference

FIAT 124 Spider

ECU CU97X CU97X CU96X CU96X

Injection Valve 0 280 150 127 0 280 150 127 0 280 150 121 0 280 150 121

Injection Valve Seal 1 280 206 702 1 280 206 702 1 280 206 702 1 280 206 702

Injection Valve Seal 1 280 206 703 1 280 206 703 1 280 206 703 1 280 206 703

Fuel Filter 0 450 905 030 0 450 905 030 0 450 905 030 0 450 905 030

Fuel Pump 0 580 464 019 0 580 464 019 0 580 464 019 0 580 464 019

Air Flow Meter 0 280 202 023 0 280 202 023 0 280 202 023 0 280 202 023

Auxiliary Air Valve 0 280 140 120 0 280 140 120 0 280 140 120 0 280 140 120

Cold Start Vale 0 280 170 041 0 280 170 041 0 280 170 041 0 280 170 041

Combi-Relay 0 332 514 127 0 332 514 127 0 332 514 121 0 332 514 121

1983 1982 1981 1980

Thermo-Time Switch 0 280 130 214 0 280 130 214 0 280 130 214 0 280 130 214

Oxygen Sensor
w/Connector 0 258 001 051 0 258 001 051 0 258 001 051 0 258 001 051

Pressure Regulator 0 280 160 214 0 280 160 214 0 280 160 214 0 280 160 214

Temperature Sensor
Coolant 0 280 130 023 0 280 130 023 0 280 130 023 0 280 130 023

Throttle Switch 0 280 120 300 0 280 120 300 0 280 120 300 0 280 120 300

53

Engine Maintenance + Modification

FIAT 124 Spider

5.13 Diagnostics and Troubleshooting

5.13.1 Air Input Diagnostics

Air leaks are the single most common cause of fuel injection system problems. Air
entering the system from any part of the engine not connected to the fuel injection
system is “false air” – it is entering the engine in an unknown quantity and state, and
causing problems with the air/fuel ratio calculations.

If you are experiencing problems with the L-Jetronic system, start with air. Use a can of
fuel injection or carburetor cleaner spray around the various hoses, clamps and around
the injector seals. Spray around the plenum gaskets as well. While you are doing this
the engine speed should not increase or decrease as a result of the spray. If it does
you’ve likely found a leak.

5.13.2 Sensor Diagnostics

Coolant Temperature Sensor

The coolant sensor is tested on the ECU connector. Unplug the ECU and connect an
ohmmeter between terminals 13 and ground (vehicle body). The meter should read:

Temperature (F) OHMs

14 7,000 to 12,000
68 2,000 to 3,000
176 250 to 400

If the reading is 0 or less replace the sensor. If the reading is infinity check the wires
leading to the sensor for a break. If the wires are good, replace the sensor.

The coolant temperature sensor can cause the engine to stop running. If your fuel
injected Spider is running nicely and suddenly stops, inspect the wires leading to this
sensor. Bosch makes a replacement wire and connector set that will eliminate this issue
(for the next 20-30 years, then it will become brittle and fail again!)

Thermo-Time Switch

The engine must be completely cold to conduct this test. It is easier to perform this test
when the ambient air temperature is less than 80 degrees. Disconnect connector from
cold start valve. Install a test light or voltmeter to the connector. Start the engine and
note that the thermo time switch should be on for 1 to 8 seconds while the engine is
colder than 95 degrees F. Above 95 degrees the sensor will not trip.

Cold Start Injector

The engine must be completely cold to conduct this test. It is easier to perform this test
when the ambient air temperature is less than 80 degrees F. Unbolt the cold start valve

54

Engine Maintenance + Modification

FIAT 124 Spider

from the intake plenum and place the tip in a container. Operate the starter. The valve
should spray for 1-8 seconds or while the engine coolant is under 95 degrees F. The
valve should have a fine misting spray, not a drip. If the valve fails to shut off or never
sprays replace the valve.

Air Flow Meter

The air flow sensor flap should move freely and return quickly to the closed position. The
sensor must be clean. The air flow sensor is tested on the ECU connector. Unplug the
ECU connector and connect an ohmmeter between terminal 6 and terminal 8.
Resistance should be no more than 600 OHMS. Connect an ohmmeter between
terminals 7 and 8. Resistance should be no more than 1200 OHMS. Connect an
ohmmeter between terminals 8 and 9. Resistance should be no more than 350 OHMS.

Oxygen Sensor

Connect a voltmeter to the oxygen sensor and ground. The changes are constant - under
hard acceleration and wide-open operation the sensor will read very high; under nominal
operation it will cycle between 100mV and 1000mV.

Auxiliary Air Regulator

The auxiliary air regulator voltage can be tested by connecting a test light or volt meter to
the connector poles. Voltage will be apparent when the engine is running. If voltage is
not apparent replace the double relay. The air regulator may be suspect if the vehicle is
idling poorly and all idle-related tests have been completed successfully.

Fuel Pump and Pressure Regulator

The fuel pump should never be noisy. Voltage at the pump terminals should be
approximately 12V; terminals are prone to getting dirty and cleaning them may improve
connectivity. Terminals should have rubber boots over them; if not consider covering
connections with electrical tape or silicone. Fuel pump operation can be tested by
testing the fuel line pressure in the engine compartment. Fuel feed pressure is 36 +/- 3
psi with the fuel pressure regulator disconnected. Pressure is 28 psi with the regulator
connected.

Fuel Injectors

Injectors can be tested by removing the injector and placing the nozzle in a glass
container. Operate the engine and check that the fuel spray is a mist. There should be no
drips. Injectors pulse during normal operation (see below). You can test the injector
voltage pulse with a voltmeter or test light. Disconnect an injector plug and connect to
each plug in the connector. Operate the starter (the car may or may not start) and note
that voltage should pulse - making the light flicker weakly or the voltage to fluctuate. If
there is no fluctuation then the ECU may be bad.

55

Engine Maintenance + Modification

FIAT 124 Spider

5.13.3 Troubleshooting

The Bosch L-Jetronic system is extremely reliable; however, it has been over 20 years
since the last L-Jetronic was installed in a FIAT Spider. Electronic parts fail over time,
and those exposed to the heat and filth of an engine bay are no exception. If you are
working with a newly acquired Spider or have never diagnosed all of your sensors it may
be worthwhile to go back to the “Sensor Diagnostics” section and test your fuel
injection system if you have not done so already.

Table 5: Fuel Injection System Troubleshooting

Symptom

Engine cranks but does not start

Engine starts but then dies

Rough or unstable idle

Idle speed incorrect

CO value incorrect

Erratic Running

1

•••• ••••

2

•••• ••••

3

••••••• •

4

••• •

5

•

6

•

7

••• •• •

8

•

9

•••••• •

10

•

11

••••

12

••• • •

13

•••••• ••

14

•• •

15

16

17

18

19

20

• •

••••

•••••

•••••• •

••• ••

••• • •

Cause Remedy

Engine misses when running

Fuel consumption too high

No maximum power

Defect in ignition system

Mechanical defect i n engi ne
Leaks in air intake system (f alse

air)
Blockage in fuel system
Relay defective; wire to injector

open
Fuel pump not operating

Fuel system pressure incorrect Check pressure regulator

Cold start valve not operating

Cold start valve leaking Check valve for leakage

Thermo-time switch defective
Auxiliary air valve not operating

correctly
Temperature sensor defective

Air flow meter defective
Throttle butterf ly does not

completely close or open
Throttle v alve switch defective Check with ohmmeter and adjust

Idle speed incorrectly adjusted

Defective ignition valve

CO concentration incorrect ly set
Loose connection in wiring

harness or system ground
Control unit defecti ve

Check battery, distributor, plugs,
coil, and tim ing

Check compression, valve
adjustment, and oil pressure

Check all hoses and
connections, eliminat e leaks

Check fuel tank, f ilter, and lines
for free flow

Test relay, check wiring harness
Check pump fuse, pump relay,

and pump

Test for spray, check wiring and
thermo-time switch

Test for resistance readings vs.
temperature

Must be open with cold engine,
closed with warm

Test for 2-3 kiloOHMS at 68
degrees F

Check pump contacts; test flap
for free movement

Readjust throttle stops

Adjust idle speed with bypass
screw

Check valves individual ly for
spray

Readjust CO with screw on air
flow meter

Check and clean all connections
User known good unit to confirm

defect

56

Engine Maintenance + Modification

FIAT 124 Spider

The Bosch L-Jetronic troubleshooting table is presented in the table above. It does a
good job of presenting many of the common faults with the system and giving possible
causes and remedies. This is followed by troubleshooting problems that are specific to
the FIAT Spider.

Air Flow Meter Failures

According to Bosch, any malfunction of the AFM should result in replacement. At about
$500 each, this isn’t always the best option. Some issues are easy to diagnose and
repair yourself.

A sticking intake valve can cause air from engine compression to push backwards
through the fuel injection system. The net result is often a bent AFM flap and very poor
or no running. Some Spider AFMs have an accommodation for this, a circular spring­loaded “door” in the middle of the air flow meter flap that opens with pressure. This
door often blows apart, sparing the flap. A bent flap may be repairable by bending it
back into place or, if the door bent slightly down, by sanding (with very fine sandpaper)
the aluminum surfaces inside the AFM door. A blown circular door can be fixed with
epoxy (it will no longer open, meaning you need to fix the sticking valve or problem that
caused it to blow out).

Keep in mind that if you are stuck on the side of the road due to an AFM door failure, the
circular type should leave the AFM flap workable but with a quarter-sized hole in the
middle. It can be temporarily covered with duct tape as an emergency fix. Attach to the
outside only, you don’t want duct tape sucked into your engine! This procedure works
quite well, as your author learned it the hard way.

Also note, an engine that is bending AFM flaps is going to bend the flap of any AFM you
put on the engine; the problem is in the valve train and should be repaired there before
wasting money on air flow meters.

Temperature Sensor Failure

The temperature sensor is unlike the other sensors in the fuel injection system in that,
when it fails, the car typically will not run. Many times this problem is diagnosed as the
sensor and a replacement occurs. This sensor is in a very hot part of the engine,
exposing the sensor and wiring to harsh conditions. It is important to inspect the wiring
leading to this sensor and make sure it is in very good condition. A replacement
connector and wiring is available to splice it if there is any question.

Click-Click-Clicking Double Relay and Fuel Pump Eccentricity

Assume you are driving along and, while at or near idle, you hear a very rapid click-click­click-click (etc!) coming from the passenger side of the car. The double-relay is likely
turning on and off very quickly. This is the result of the fuel pump switch in the air flow

57

Engine Maintenance + Modification

FIAT 124 Spider

meter being set too low, so that the pulse of air during idle keeps turning the pump on
and off. Adjust the rod as described in the “Air Flow Meter Failure” section above.

The fuel pump may begin behaving erratically or running “all the time” (draining the
battery). The pump is activated by a chrome rod inside the air flow meter. When the
AFM flap moves the pump turns on. Therefore when your engine is cranking, idling, or
cruising, the pump is on. Over time the rod may move out of position; it can be fixed by
lifting the black cover off of the AFM and bending the rod so that the pump is on only
when the flap has moved.

58

Engine Maintenance + Modification

FIAT 124 Spider

6. The Cylinder Head

If you open your hood and look at the center of the engine you’ll see four spark plugs.
The aluminum thing that your spark plugs are screwed into is the cylinder head. The
cylinder head on a FIAT 124 Spider is of the semi-hemispherical, dual overhead cam
(DOHC) type. It is called semi-hemispherical because the operation occurs along a 180
degree arc. The two camshafts sit on either side of the spark plugs and rotate in time
with the engine main crankshaft to draw in, burn, and expel fuel. A cylinder head has
three major components:

Camshafts are metal poles with lobes on them. The lobes press against valves
that open and close, allowing gases into and out of the engine. Lobes are
engineered into a specific pattern, resulting in the camshaft being the
mechanical brain governing the Otto cycle.

Valves cover ports between the intake and exhaust manifolds and the
combustion chamber. Valves are held closed by a high tension double-spring
assembly. The spring is held down by retainers installed in a donut-shaped cap.
The entire assembly is capped off by a bucket. The camshaft strikes a shim on
the top of the bucket, opening the valve. The shim is adjustable to maintain
proper valve clearance.

Spark plugs descend into the combustion chamber and create a spark that
ignites the air/fuel mixture.

We start this section with the intake of fuel from the fuel system and finish with the
expulsion of spent fuel into the exhaust system. Assume your engine is just starting the
intake cycle – the camshaft has depressed the intake valve, drawing air and fuel into the
combustion chamber (figure 41.1). As the camshaft rotates the valve closes. The piston
is pushed upwards, compressing the mixture (figure 41.2). Ignition occurs (figure 41.3),
exploding the mixture and forcing the piston down. Finally, the camshaft opens the
exhaust valve and the piston is drawn up, expelling the burned mixture (figure 41.4).

59

Engine Maintenance + Modification

Figure 41.1: Intake Figure 41.2: Compression

FIAT 124 Spider

Figure 41.3: Ignition Figure 41.4: Exhaust

The diagrams above show the absolute end or beginning of each cycle. The duration of
time that the valves remain open and the timing of when each valve opens are
determined by the shape of lobes on the camshaft. On the FIAT DOHC there are two
camshafts, each with four lobes (one per valve, two banks (intake and exhaust)). The
camshaft lobes move through the four phases for each 90 degrees of rotation. In a
DOHC engine the opposite camshaft is in the same position and having the opposite
action; in other words, when the intake camshaft is in the intake position the exhaust
camshaft would be at the same angle, performing no action on the exhaust valve.

60

Engine Maintenance + Modification

66393

381968

9899

381969

000

608

Sport Spide

000

60819

Coupe

385

0

Sport Spide

000

608

Coupe

000

608

Coupe

68803

000

60819

Sport Spide

590

3

5619

Coupe

59

973-19

56Late

d

e

99513

608Early

8553

34AC.6C

56Lancia Scorpio

56, 1995

9951980 Lancia Beta

56, 1995

995

99513

9951979 131 & Beta Coupe

396

99579

a

599

9951984 Spide

FIAT 124 Spider

6.1 Cylinder Head Identification

Cast into the top of your cylinder head is an embossed identification number. Because it
is possible (and oftentimes desirable) to install an earlier cylinder head on some blocks,
you need to identify if such a swap has occurred on your engine.

Table 6: Cylinder Head Casting Number Table

Casting Number Other Casting ID Displacement Comments

41

124AC 14

41

4 124AC 14

4232871 124AC.

4232974 124AC.

42

27 132AB.1A.

4239436 124AC.

4239436 124AC.

42

124AC.

4277

1

4304781 132AC.OC 1

4314402 17

4325215 1

4326319 124AC 1

434

1

4371507 132.C8.1A0 1592, 17

4372281 1

4372291 134AS 17

4372297 1592, 1

4372748 1

4406111 132AC.2C 1

44

44 132AC.2C 1

2129 1

1

1

1592

1

1

1

2AB.9A 17

21

17

http://www.mirafiori.com/faq/content/headid/headid.html

124 Spider

124 Spider

r

72 124

124

124

72-73

74-76

124 Spi

1

124

131/132 and 1981-82 Spider

1977 Spider

131

1

Brav

r

r

74 Spider

r

n

r

Pete Angel maintains the table above and has made these additional comments on head
identification:

• The 1438 twin cam head is lacking an additional water passage on the intake

face, rear of the #4 intake port. All other heads have a water passage there. This
makes other intake manifolds incompatible on the 1438 unless the water

61

Engine Maintenance + Modification

FIAT 124 Spider

passage in the manifold is blocked. Conversely, the 1438 manifold cannot be
used on the other heads unless the passage in the head is blocked.

• The center-to-center combustion chamber spacing is the same on all heads. The

combustion chamber sizes vary with the USA 2000cc amongst the largest,
affording the lowest compression ratio.

• The 1438 and 1608 heads can be distinguished from other twin cam by the size

of the water passage on the head face in front of cylinder #1. The width of this
passage on these heads is 14mm (0.55"). The 1592cc, 1756cc & 2000cc heads
have a 9mm (0.35") wide passage. Because of this, the 1438cc & 1608cc heads
will not work on the 84 mm bore engines unless this water passage is welded.

• The exhaust port size is nearly identical on all DOHC heads. The intake port size

varies. Generally, the smallest port size is found on the 1438cc. The 1608cc,
1756cc & Volumex heads share approx the same, large intake port size.

62

Engine Maintenance + Modification

FIAT 124 Spider

7. Intake Manifolds

FIAT used two types of intake manifolds on carbureted engines. The type of manifold
was relative to the type of carburetor. Carburetors fitted with a vacuum operated
secondary barrel (those with an “H” in the name) were fitted with a manifold with
different sets of upper and lower runners. These can be identified by removing the
carburetor and noting that the two barrels have their own plenums, instead of one large
opening underneath the carburetor base. When using the vacuum type carburetors it is
important to have the dual planes for proper opening of the secondary barrel; when using
the non-vacuum carburetors the split planes will impede performance. Therefore it is
important to have the correct manifold for your carburetor and, if you are planning a
swap to another carburetor, that you are also planning for a manifold swap.

Table 7: Intake Manifold Casting Numbers

Part Number Original Fitment

4186411 1438cc 1967-1968

4226586 1438cc 1968-1970

4242994 1608cc 1971-1973 (Dual IDF)

4248067 / 4248068 1608cc 1971-1973

4304461 1592cc 1973

4308888 1756cc 1974

4334447 1756cc 1975-1978

4406112 2000cc 1979-1980 (Carbureted)

4468499 2000cc Fuel Injected

63

Engine Maintenance + Modification

FIAT 124 Spider

8. Exhaust System

The exhaust system conveys spent gasses from the cylinder head to the exterior of the
car. Exhausts perform a number of valuable functions and exhaust design is crucial to
good engine performance. Emissions, noise, and backpressure are key concerns in
exhaust design. Emissions must be safely conveyed away from the passenger
compartment; in the case of the FIAT Spider they are reduced by a catalyst and expelled
behind the vehicle. Noise produced by an engine must be muffled in order for the
vehicle to function in society; therefore a muffler is installed at the rear of the vehicle to
reduce exhaust noise. Spiders also have a center resonator, an additional muffling
device located above the rear axle. Backpressure exists if gasses escaping the engine
meet resistance and, taking into account the safety and environmental features noted
above, is the focus of good exhaust system design.

A poorly-designed exhaust manifold may create pressures that inhibit the engine’s ability
to breathe. Many vehicles have intricate exhaust systems, designed specifically to
equalize the length of each cylinder’s exhaust pipe. FIAT Spiders used two types,
known as 4-2-1 and 4-1; the former is considered to be a superior design. Aftermarket
headers are also produced, each touting improvements to the original designs (with
dubious pedigree; refer to the section titled “improvements” later in this book.)

There are two types of the 4-2-1 design. The first was fitted to 1756cc Spiders
manufactured in 1974. There are four pipes running from the exhaust side of the engine,
tapering down to where a flanged two-pipe fitting mates and extends under the car.
Here a single pipe leads through a catalytic converter (or not, depending on year),
through mufflers and out of the car. The second type of 4-2-1 was installed on the fuel
injected Spiders. It is similar in design except the four primary pipes bend into two and
into a collection “box” where the oxygen sensor is installed. The 4-2-1 was designed for
Spider engines in the 100+ HP range and is at least as good (arguably better) as most
“performance” aftermarket systems.

The 4-1 design was installed on most Spiders and in every engine displacement. Four
short pipes extend from the exhaust manifold into a single pipe that runs under the car
to the catalyst and onwards. The design is simple and the exhausts are very well built.
They suffer only from the rather abrupt turns from the exhaust ports to the down pipe
and, unless the engine is going to produce more power than stock, may not be worth
replacing.

8.1 Exhaust System Identification

Look in your engine compartment at the exhaust side of the engine. There may be a
metal heat shield on top of the exhaust - it will have three 13mm nuts securing it down.
The exhaust system parts have the part numbers stamped into them. It is very unlikely
that a Spider will have the original parts from the down pipe back.

64

Engine Maintenance + Modification

Table 8: Exhaust System Casting Numbers

Year Manifold Header Pipe Intermediate Muffler Rear Muffler Note

FIAT 124 Spider

1967

1968

1969

1970

1971

4151276

4151276

4151276

4151276

4151276

4310530 4401843 4285627

4310530 4401843 4285627

4310530 4401843 4285627

4310530 4401843 4285627

4310530 4401843 4285627 1438cc

1971 4166429 4310530 4401843 4285627 1608cc

1972 4166429 4310530 4401843 4285627

1973

1974

4166429

4308891

4310530 4401843 4285627

4310530 4401843 4285627

1592cc

1975 4314919 4341428 4341867 4285627 California

1976 4314919 4341428 4341867 4285627

1977 4380776 4341428 4341867 4285627

1978 4377811 4341428 4341867 4285627

1979 4407872 4419699 4419683 5976218

1980 4407872 4419699 4419683 5976218

1980 4462282 4443328 4443325 5976128 California

1981-1985 4462282 4443328 4443325 5976128 To Chassis 5506060

1981-1985 4462282 7531187 4443325 5976128 From Chassis 5506061

65

Engine Maintenance + Modification

FIAT 124 Spider

9. Ignition

The ignition system in your FIAT is one of four types, all of which operate according to
similar principles. For the vast majority of Spiders, a distributor is mounted on the rear of
the cylinder head. Some early Spiders were fitted with distributors that run off of the oil
pump gearing. In both cases a shaft inside the distributor body spins in time with the
engine camshafts. The drive shaft turns a metal-tipped rotor that strikes connectors
inside of the distributor cap. When contact is made an electrical connection between
the spark plug and the distributor coil is made, sending a current from a high energy coil
and generating a spark that ignites the fuel mixture in the combustion chamber. As the
distributor rotates through its cycle the electrical pulse is sent to the tachometer,
resulting in a reading of engine speed in revolutions per minute (RPM).

The 1967-1972 Spider had a simple “single point” distributor, where a single set of
points was activated by the movement of the distributor shaft. From 1973 (on the
1592cc engine) through 1978 FIAT used a “dual point” distributor, where one set of
points was used for starting and another for running. The first set (the starting set)
created additional advance during starting. After 1978 an electronic system was used.
The points used in prior models were replaced with devices that electronically controlled
the spark and vacuum controlled the advance. A fourth system was made available by
FIAT for a brief period of time, and is coveted by many Spider owners. The Marelliplex is
a mechanically-advanced electronic distributor. To a Spider owner it eliminated the
dependence on the throttle-controlled vacuum pulse of the stock electronic unit, yet
used all stock components otherwise. All four systems are extremely reliable when
properly maintained.

9.1 Ignition Components

For our purposes, the major components of the ignition system are the coil, distributor,
spark plugs, and wires. Depending on the type of system (electronic or mechanical)
there are other pieces and parts, such as points, condensers, magnetic pickups, and
control modules. We’ll cover the important pieces that you need to understand in
getting to know your Spider.

The Coil stores electrical energy. It is a cylinder bolted to the firewall and is easy to spot
as it has one big wire coming from the top and smaller wires from either side. On
Spiders made from 1979 to the end of production the coil was part of a pack that
included a finned housing and control module.

The Distributor is an electrical switch, using engine rotation to propel a rotor against a
series of contacts. As the distributor shaft turns an electrode on the rotor makes the
connection between the coil and each of the spark plug wires. A set of points (1967-

1978) or a magnetic pickup (1979-1985) releases energy from the coil into the wires.

66

Engine Maintenance + Modification

FIAT 124 Spider

Spark Plugs have electrodes suspended in the combustion chamber and are connected
to a cap on top of the distributor by wires. When the distributor releases the coil’s
energy it travels through the cap, into plug wires, and into the spark plugs. The resulting
spark ignites the fuel/air mixture in the combustion chamber.

Plug Wires are designed to contain the high energy of the coil and deliver it to the spark
plugs. They are the largest wires in the engine compartment and are quite obvious as
they run the top of the cylinder head.

Points are small electrical switches that open and close as the distributor rotates. When
the points are closed an electrical field builds up in the ignition coil. When they open the
field collapses, releasing energy into the spark plug.

A Condenser is a small (typically silver) barrel on the body of the distributor. It absorbs
misdirected (for lack of a better term) energy that runs from the coil back to the points
instead of to the spark plugs. Without a condenser the points will deteriorate quickly or
weld themselves together.

The Magnetic Pickup is the equivalent of points on the electronic ignitions installed in
the 1979-1985 Spider. Instead of the striking motion and inevitable wear associated with
points, a magnetic pickup literally “picks up” the increasing and decreasing magnetic
wave created by lobes in the distributor shaft. The energy from the coil is released by a
control module located on the coil itself.

The Control Module is located on the coil pack of the 1979-1985 Spider. It
electronically collapses the coil’s electrical field.

The Vacuum Module is a dashpot located on the side of the 1979-1985 Spider
distributor. A diaphragm inside the dashpot is connected to a shaft that pulls or pushes
the advance plate. The diaphragm is moved via vacuum pulse from the throttle body.
On fuel injected cars it is connected to a port located near the throttle on the air flow
meter side of the throttle plate. On carbureted Spiders the port is located just above the
throttle plates. In both cases when the throttle opens a drop in air pressure pulls on the
diaphragm which in turn moves the advance mechanism.

9.2 Ignition System Identification

All Spiders made prior to 1979 had breaker points. A single-point distributor will have a
coil mounted to one of the inner fenders and a single condenser on the distributor body.
It is the least complex of the Spider ignition systems. A dual-points distributor is similar
to the single-point but has two condensers on the body and two sets of points on the
interior. Some 1973-1978 Spiders have had the dual-points removed (replaced with a
single point internally) or the entire distributor replaced with the single-point model. The
single and dual point distributors can be identified externally; single-point distributors
have a single condenser and wire (blue/black) running off of the distributor. Dual-point
distributors have two wires (green and green/black). The coil for both units is a common

67

Engine Maintenance + Modification

FIAT 124 Spider

barrel type mounted to the inside of the driver’s side fender on the early models and the
passenger side on the late models.

The electronic ignition system of the 1979-1985 Spiders can be identified by the large
coil pack mounted on the passenger side fender wall. If stock it will have an enclosure
of aluminum fins to each side and a control module on the bottom back. Most electronic
distributors will be stock, with a vacuum canister mounted on the side. Two wires
wrapped in a small diameter tube run from the distributor pickup to the coil pack. The
now rare FIAT replacement part known as the Marelliplex system looks identical except
that it has no vacuum canister on the side of the distributor (and no way to install one; a
sure way to identify a fake Marelliplex is to see if the base has the opening and fitting for
the vacuum dashpot).

Table 9: Ignition System Components

Breaker
Points or

Series Seal Cap Rotor Condenser

Pickup Unit Coil Unit

AS 9915908 9925467 9924654 9913848 9913862

BS1 9921512 9925467 9924394 9922454 7111161

CS1 9921512 9925467 9924394 9926424

(74-77)

9929180 (73)

CS2 9921512 46340 56290 859818 9937730 4386220

CS0 9921512 46340 56290 859818 9937730 4386220

DS0 9921512 46340 56290 859818 9937730 4386220

7111161

9.3 Ignition Advance

In your Spider the basic ignition timing is set to either 5 degrees (1438cc), 0 degrees
(1592cc, 1608cc 1756cc) or 10 degrees (1978 1756cc and all 2000cc) behind top dead
center (BTDC). This means that the spark plugs “fire” when the crankshaft angle is
almost at the absolute top of travel. This is called ignition advance. Advance is a term
applied to timing an engine in such a way that the spark is delivered just before the
piston reaches top dead center. This is necessary because there is a time lag between

68

Engine Maintenance + Modification

FIAT 124 Spider

when the spark is delivered and the fuel/air mixture and cylinder pressures are optimal.
If the spark occurs at top dead center then the piston is already moving down when
these optimal conditions are possible. Therefore the spark is forced to occur just prior to
top dead center; the fuel/air ignition begins and reaches its maximum at the appropriate
time.

A variation in ignition advance is required to maintain optimal efficiency. Beyond the
“hard” setting of 0 or 10 degrees BTDC the ignition distributor has a metal plate that
moves according to engine speed. This movement, governed by either centrifugal or a
combination of centrifugal and pneumatic force, varies the advance so that the spark is
delivered at the optimal point, up to 32 degrees BTDC (depending on series, some were
limited to 28 degrees).

Spiders manufactured prior to 1978 have centrifugal advance plates, the movement of
which is driven by the spinning of the distributor shaft. As the shaft increases in speed
the centrifugal force moves the advance plates outward, increasing the advance.

On Spiders manufactured after 1978 (the CS2, CS0, and all Pininfarina Spiders) the
vehicles were fitted with a Marelli electronic ignition with a pneumatically-operated
advance mechanism. It has often been misidentified as a pollution control – it certainly is
not. The diaphragm in the distributor varies the amount of advance when it is pulled by
the drop in air pressure that occurs when the throttle opens. As the throttle opens and
more air enters the engine the amount of advance increases. This design makes the
ignition advance dependent on the actual load of the engine rather than the speed of the
engine; arguably a more efficient design.

9.4 Firing Order and Initial Timing

All FIAT Spiders fire in the order 1-3-4-2. The initial timing is set so that the camshafts
and crankshaft are in the initial position, with camshafts aligned with pointer holes and
crankshaft aligned to the block mounted pointer. When this initial position is met the
engine is set to fire on the #4 cylinder (figure 43).

Crankshaft Camshaft Distributor Rotor Position

PULLEY TIMING MARK IS
AT 0° BTDC

Figure 42: Initial Ignition Setting

69

Engine Maintenance + Modification

FIAT 124 Spider

A nut holds the distributor shaft down on the engine block or cam box. To turn the
distributor (the engine does not need to be turned on at this point), simply loosen the nut
so that the distributor rotates. It is useful to loosen it only enough so that it will turn,
some tension is desirable and holds the unit in place while you turn the distributor.

Once the initial settings are correct you’ll need to set the ignition timing to the running
position. This varies between engine types as described in the table below:

Table 10: Ignition Advance by Engine Type

Motor Degrees of Advance BTDC

1438cc, 1608cc 5

1592cc 0

1796cc 0

2000cc 10

If you removed the distributor cap and wires in the previous setting you’ll need to re­install them now. You should keep the distributor loose enough to rotate since you’ll
need to rotate it again.

Start the engine and let it run until it reaches 190 degrees F (usually two complete cycles
of the fan). If the engine will not run rotate the distributor slightly in either direction until
it will run, or increase the idle speed screw to hold the throttle open. Once 190 degrees
is reached reduce the idle speed to approximately 850 RPM or 900 RPM for engines
with air conditioning.

Timing Light Engine Speed

850 +/- 50

(w/o AC)

900 +/- 50

(with AC)

Figure 43: Final Timing (2000cc engine)

70

Engine Maintenance + Modification

FIAT 124 Spider

There are two methods you can use to set the initial ignition timing. One is “by the
book,” meaning you set it just like FIAT tells you to and lock it down. The second is to
set the ignition timing by ear. There are advantages to both methods – your goal needs
to be to set your engine to the point where it runs best, which may be “by the book”
and may be “by ear.”

The “by the book” method is to take the ignition advance information from the black
metal plate inside your hood (if it isn’t there then use the information in table 10 above).
FIAT varied the timing data (to meet emissions regulations) enough that you want to rely
on your car’s data plaque if you can. Using a timing light on the #1 plug wire, start the
engine and point the light at the crankshaft position marker. Rotate the distributor so
that the timing is set per the crankshaft marker (see Figure 43). The engine speed may
increase or decrease while setting the timing; adjust the carburetor idle speed screw
accordingly to maintain the correct engine speed.

The “by the ear” method disposes of the need for a timing light. Once your engine is
set to zero degrees BTDC you will advance the distributor to the point at which the
engine speed is no longer increasing. Advancing the distributor improves combustion,
resulting in increased engine speed, but at some point it is too much and a reduction
occurs. Once the reduction begins retard the ignition until the engine speed is at the
highest point without missing or puffing. Set the idle speed to the appropriate RPM.

In both cases you want to drive the vehicle and check what you’ve done. If you’ve tuned
by the book you need to check the timing again with a light. If you’ve tuned by ear then
make sure engine operation through acceleration and deceleration is nice and smooth.
The ignition may be advanced too much (remember, the distributor further advances
once it gets moving) and require you to retard it a few more degrees to get it all correct.

There is a third method – where you tune to the desired maximum advance. Richard
Ridge submitted the following on my queries about ignition timing:

[What is optimum timing?] It is the timing that allows the car to start readily and smoothly accelerate
while also delivering the highest peak torque possible under full load. And of course it also has to meet
whatever emissions limits are required. It is not a single number, rather it is a curve, a smooth timing
advance progression from a few hundred rpm to the rpm at peak torque.

The actual numbers depend on cam timing, compression, head work, induction and exhaust
configuration. Accuracy requires dyno work or trial and error on the street. Looking at the factory curves
for different engine configurations is a good way to start.

For a race engine that has no real starting, drivability or emissions restrictions, the answer does boil
down to a single number. Others have suggested that for TC engines in typical competition trim, the
number is in the 35-38 degree BTDC range.

Given this information, if you want to seek out a specific degree of maximum advance
you need to determine the maximum advance of your distributor, do a little math, and
figure out your initial timing. If you want 35 degrees of advance and have a distributor
with 30 degrees of total advance, your initial timing will be 5 degrees. Sounds simple,
right? Trial, error, and patience will pay off if this kind of accuracy interests you.

71

Engine Maintenance + Modification

FIAT 124 Spider

The block mounted distributor on Spiders made prior to 1971 has approximately 5
degrees of fixed advance with a maximum of 29 degrees of variable advance. The
advance increases in a linear manner to its maximum at 3500 RPM.

The camshaft mounted distributor on the 1971-72 Spider has approximately 5 degrees of
fixed advance with an additional 24 degrees of variable advance. The variable advance
increases in a linear manner from approximately 0 degrees at 850 RPM to 31 degrees at
4300 RPM.

The 1974 – 1978 distributor has approximately 10 degrees of fixed advance with the first
(starting) set of points and 0 with the second (running) set (at 850 RPM). Normal running
occurs on the first of points, with centrifugal advance to a maximum 36 degrees at 3500
RPM. The running points are activated when full oil pressure is reached and the water in
the intake manifold passages begins to increase.

Dave Voss, a FIAT owner who took the time to disassemble and understand the
differences in the 1979-1985 vacuum advance (electronic) distributors, noted the
following:

Given the age of these distributors, and the high likelihood that swaps and rebuilds have occurred
along the way, your [electronic] distributor could be any one of 6 combinations:

47º total = 33º mechanical + 14º vacuum
43º total = 33º mechanical + 10º vacuum
33º total = 33º mechanical + 0º vacuum (failed or disconnected)
36º total = 22º mechanical + 14º vacuum
32º total = 22º mechanical + 10º vacuum
22º total = 22º mechanical + 0º vacuum (failed or disconnected)

The distributor top plate, under the rotor, is stamped with the degrees of mechanical advance. The
vacuum canister is also marked. Generally speaking the replacement parts available today are for the
49-state version and, unless pinging or knocking occurs during operation, the 49-state is appropriate
for all Spiders. The electronic system also fits earlier models and is often found under the hood of
many older Spiders.

To recap, ignition advance is a crucial concept in tuning. A recommended approach is to
set your engine “by the book” and, as you understand more about your vehicle and your
driving needs, begin to adjust “by the ear” or to the maximum advance. FIAT
distributors interchange easily between vehicles, so the advantages of an electronic
system on an older motor may be appealing, or using a single-point distributor on a mid­year Spider.

9.5 Ignition Electrical Diagrams

Note: These diagrams are excerpts from the electrical system diagrams I have produced
for each FIAT Spider model year. The diagrams are available online at

http://www.artigue.com/fiat

.

72

Engine Maintenance + Modification

FIAT 124 Spider

Figure 44: Ignition Electrical Diagram for the 1967-1973 Spider

IGNITION SWITCH

15/54

PINK

BROWN/

WHITE

30 87 87a

IGNITION MODE

RELAY 128/2

GREEN

C40

GREEN
/BLACK

LT BLUE/

BLACK

+B

D

BROWN

C15

DISTRIBUTOR

1

C9

1

3

42

2

3

4

Figure 45: Ignition Electrical Diagram for the 1974-1978 Spider

73

Engine Maintenance + Modification

Figure 46: Ignition Electrical Diagram for the 1979-1985 Spider

FIAT 124 Spider

9.6 Diagnostics and Troubleshooting

9.6.1 Electronic Ignition Failures

Vacuum Capsule

The failure of this capsule causes poor acceleration. With the engine running you should
see the shaft between the dashpot (the barrel on the distributor body) and the distributor
pulse. If someone presses the accelerator pedal you will see the shaft pull the shaft
back towards the hose. If not then consider that air pulled through the hose (away from
the dashpot) will move the shaft if the unit is operating properly. This is not to suggest
you suck on the air hose – if you do and the diaphragm is broken then you will suck in
the paper and other dirt from the busted diaphragm.

Note that some FIAT owners suggest that their car works fine with this unit
disconnected or inoperable and the distributor manually advanced; you cannot
your vehicle properly with this unit inoperable. It is far more likely that these owners
have forgotten what the car is like with the advance mechanism working properly!

Ignition Pickup

set up

The pickup wires can become hard and brittle over time. Wires may also ground on the
distributor body. Both situations typically cause poor running and the tachometer may

74

Engine Maintenance + Modification

FIAT 124 Spider

be erratic during operation. Inspect the wires at every oil change and change if they are
suspect.

Rotor or Cap Failure

Old, brittle, or over-tight rotors can explode inside the distributor cap. They can spin
themselves to pieces. The contacts inside distributor caps can also become brittle over
time, as can the cap itself. Inspect and change them when necessary.

9.6.2 Conventional Ignition Failures

Points and Condensers

Poor operation, acceleration, and other running problems may be due to worn points.
Inspect the points for the appropriate gap and dwell. Check that the points show even
and not excessive wear. When replacing, change the condenser(s) at the same time.

9.6.3 Common Ignition Failures

Spark Plugs and Wires

Bad plugs and wires can arc, causing misfires and poor overall operation. Plug wires
should not be brittle or have any corrosion on the contacts. At night with the hood open
you should see no arcs between the wires and the engine body. There is no substitute
for high quality 7mm or 8mm wires like Magnecor or Bosch. The spark plugs should be
of the resistor type and free of corrosion. When removed from the engine they should
be very clean and with a brownish-white “burn” on the electrode.

Coil

Missing or poor combustion can be caused by a malfunctioning coil. The coil and
electronic coil pack are extremely durable and reliable units. The shop manual has
procedures for testing each unit. When replacing do not use any coil unit on the
electronic system not specifically designed for this purpose.

Poor Operation and Erratic Tachometer Display

Poor operation accompanied by a tachometer that is jumpy or otherwise erratic is often
caused by a short circuit inside the distributor body. On both electronic and conventional
distributors this may be caused by a broken rotor or metal in the cap. On the electronic
distributor this is usually caused by the wires leading to the pickup unit becoming frayed
and interfering with the metal advance plate.

75

Engine Maintenance + Modification

FIAT 124 Spider

10. The Major Tune Up

A major tune up is something you should have the knowledge and tools to do, or be
willing to learn. The procedures described in this section will have you completely “re­set” your car, leaving you with a vehicle tuned to the factory specification and with all
new fluids. The idea is that you need your car to a neutral or baseline position before
trying to make any additional changes.

10.1 Preparation

Using the information you’ve already gathered (engine type, head type, etc.) you are
already on your way to establishing a baseline for your engine’s performance. It is
important to get a feel for how your existing setup operates before trying to change
anything. All of this work is easy and, armed with a shop manual for your model year;
you can do this in a couple of hours in your garage with minimal parts expense.

A suggestion before you begin: if you are new to working on cars or new to your FIAT
and note that the overall condition of your car is “worn” then consider the likelihood that
the replaceable parts under your hood are also worn. Be prepared to inspect and
purchase all of the ignition parts, hoses, shims, and belts. The expense will be minimal
and you’ll likely transform a “worn” car into one that performs just fine.

10.1.1 Ignition System

As necessary, you will need to install new plugs, wires, distributor cap, rotor, vacuum
advance capsule and hose, coil, pickup, points, and condensers, and set the timing, plug
and point gaps, and the dwell angle. Set the ignition timing to exactly what your car’s
instruction book calls for. If you have Marelli electronic ignition (1979-1985) check that
the vacuum advance is working properly. For each of these items follow the procedures
below.

Spark Plugs: If they look old, grimy, dirty, or anything but clean, replace them. You do
not need fancy spark plugs in your FIAT; your best bet is to use stock equivalent plugs
(some vendors actually sell the original equipment Marelli CW78LP, CW7LPR, and
CW67LPR and FIAT 1L4JR plugs). Spark plug gap for resistor plugs is 0.7 to 0.8mm.

Note: if the spark plugs have a greenish-white crystallization on them you likely have a
leaking head gasket that must be replaced before continuing.

Plug Wires: Brittle, hardened by heat, cheaply made, home-made, or unknown quality

wires should be replaced. As with the spark plugs you do not need an expensive set of
wires; the stock type works fine. When installing plugs coat the inside of the spark plug
boot with dielectric grease available from your auto parts store. If you like original parts
the Cavis ignition wires are available from some of the parts vendors.

76

Engine Maintenance + Modification

FIAT 124 Spider

Distributor Cap: If your cap has any cracks or shows obvious signs of wear on the
electrodes then it is time for replacement. Aftermarket caps are sometimes of poor
quality; if you can find the original Marelli distributor cap it is always your best bet.

Rotor: Replace with cap or if the wear is excessive. Spend the time to find an original
Marelli rotor; they are of much higher quality than most of the aftermarket types.

Vacuum Advance Capsule: The rod from the distributor body into the capsule should pull
when the throttle is engaged. Otherwise replace the hose, capsule, or both.

Coil: Test the coil using a voltmeter and the procedure described in the shop manual for
your model year. A twenty or thirty year old coil may still be producing good spark –
these are very durable devices. Note that the coil in the 1979-85 Spiders must be
replaced with the appropriate Marelli unit and never with a coil designed for points-type
distributors.

Magnetic Pickup and Control Module: Any wear or exposed wiring should prompt you to
replace the unit. The wires on many aftermarket units are longer than necessary, be
careful to position them so they do not rub against the moving parts of the distributor. If
you are replacing the magnetic pickup you may want to consider replacing the control
module; however, the control module is reasonably insulated and has no moving parts
near it, it tends to last much longer.

Points: For cars with breaker points, the gap should be 0.31 to 0.49mm and the contacts
should be in good condition. Marelli points are available for (at the time of this writing)
under $10.00 a set.

Condenser(s): Replace any time you replace the breaker points.

Dwell Angle: The dwell angle is 55 degrees. Check and adjust with the points.

10.1.2 Cylinder Head

The cylinder head should be checked for fluid leaks. If the head isn’t clean enough to
inspect it then consider cleaning it up with engine cleaner or carburetor cleaner. Check
the coolant hoses entering and exiting the head. Remove the camshaft covers. If the oil
inside the camshaft boxes is foamy or a milky brownish-black you most likely have a
leaking head gasket. You may also have a greenish-white crystallization on your spark
plugs. You must

replace the head gasket before using this engine.

If everything looks good then check the valve lash:

• Intake : 0.45mm cold

• Exhaust: 0.50mm cold

77

Engine Maintenance + Modification

FIAT 124 Spider

Adjust, if necessary, by using the procedure described in the shop manual. Good valve
lash is essential for engine performance.

10.1.3 Fluids

Coolant: Inspect the cooling system hoses for any cracks or hardness. If the age of the
hoses is unknown or the condition questionable then replace them all. Replace the
thermostat at the same time unless you are certain it is operating properly. Make sure
and check the heater hoses to and from the cylinder head and, on the fuel injected and
water choke carbureted vehicles, the small hoses running from the intake manifold and
heater pipe to the carburetor/fuel injector plenum. Fill the system with the appropriate
mixture of coolant and distilled water.

Keep in mind that the FIAT cooling system is particular about how it is filled. There are
two popular procedures that you can do in your garage. Open your heater valve prior to
performing either method:

• The first is to place the front of the car on ramps or jacks and get the level of the

radiator cap higher than the back of the cylinder head heater hoses (in the back of
the head is a black hose that runs up near the #4 plug and then behind the head). Fill
the system from the radiator.

• The second method is (in your author’s opinion) the most effective. Using a flush-

and-fill kit (such as the Prestone Flush and Fill Kit) install the filler “T” in the cylinder
head heater hose. With the radiator cap off fill the system until water comes out of
the radiator. Install the radiator cap. Now loosen the brass cap at the radiator hose
intersection in front of the head and fill until coolant flows from this point. Tighten
and finally top off to the “T”.

Oil: Your FIAT was designed to use a FIAT branded oil called Oliofiat. Oliofiat VS+ 15W­40 was the typical specification for the Spider. The oil carried an API rating of "SE",
which at the time was the highest rating for automobile and light truck use. The current
rating is "SJ" and any oil in the SAE 10W-30, 10W-40 or 20W-50 viscosity range that
carries the current "SJ" service rating will suffice.

Gasoline: If your gasoline is old or questionable then siphon your tank to empty and fill
with the highest octane you can purchase from a gas station. Do not use fuel additives.

10.1.4 Filters

Replace the air cleaner filter if it is dirty. On carbureted vehicles replace the fuel filter
with a glass type having a replaceable element. On fuel injected vehicles replace the
fuel filter with a new Bosch filter.

If you suspect any kind of fuel flow problem remove the fuel tank sending unit and
inspect the mesh screen filter inside the tank. There is also a small filter on carbureted
engines located inside a large brass nut on the fuel intake assembly of the carburetor

78

Engine Maintenance + Modification

FIAT 124 Spider

(typically on the bottom, refer to your carburetor diagram). It can be removed and
cleaned with carburetor cleaner.

10.2 Tuning Procedure

Here are the steps to get your engine tuned to the factory specification. Note that the
three steps really just refer you back to the proper section. What is important here is to
not go beyond the factory setting. Don’t “tune by ear” (yet) or “dial in” anything. The
factory spec may not be perfect, but it is neutral.

10.2.1 Basic Engine Timing

Set your crankshaft to top dead center. Check that your camshaft wheels are lined up
with the markers cast into the camshaft boxes or the pointers in front of the camshaft
wheels. See the ignition section for diagrams and details.

10.2.2 Basic Ignition Timing

Using a timing light, set your ignition timing to the specification for your Spider:

0 degrees Spiders prior to 1978
10 degrees Spiders after 1978

See the ignition section for diagrams and details.

10.2.3 Idle Speed Settings

Set the idle speed according to the instructions in the carburetion or fuel injection
settings in this guide.

79

Engine Maintenance + Modification

FIAT 124 Spider

11. Improvements*

* Ask yourself if things need improving.

Performance is a relative term. You need to define how you want your engine to
perform so that it suits your needs. A high performance engine is not necessarily fast
and a poorly performing engine is not always slow. Lots of car companies state that
their engines are “high performance” just because they produce more than “x”
horsepower or “y” torque. But look at what these companies do to produce this power ­enormous V6 and V8 engines that barely produce ¾ of a horsepower per inch of engine
displacement. These can be 350 and 400 cu. in engines producing less than 300 HP.
Alfa Romeo and FIAT were producing 1HP per cubic inch of displacement in the 1960’s.
Sure, the engines produced around 100 to 120HP, but which one is higher performance?
It's up to you to define performance in terms of what you want your car to do.
Performance is relative to your needs.

Do you want to build a 200HP Spider? It can be done, with a standard FIAT engine
block, cylinder head modifications, high compression pistons, lightened flywheel and
connecting rods, supercharging, etc. Guy Croft has been building race-prep FIAT twin­cam motors from his shop in the United Kingdom for many years. He wrote a book on
the subject (which is now quite hard to find) in case you want to do it all yourself, or you
can pay upwards of $8,000.00 to get it done right by Guy personally. Alternatively, there
are numerous things you can do with a relatively stock FIAT Spider and really improve
your driving experience. The interchangeability of parts between model years allows you
to use off-the-shelf FIAT parts to truly transform your Spider.

The good news is that many Spider parts can be interchanged between engine series or
upgraded with new parts. These interchanges can be done to improve things such as
acceleration, horsepower, and torque. Parts availability and installation ease are both
very good; in other words, you may be able to mix and match parts at a minimal expense
and create an improved driving experience. This section deals with some improvements
that have been proven to be successful in delivering improved performance and
reliability.

You should approach performance improvements with some caution. There is a financial
trap you can easily fall into, with your improvements quickly reaching the point of
diminishing returns. A set of new carburetors, head work, pistons, camshafts seals,
rings, and all of the other parts can easily set you back three or four thousand dollars. It
is very easy to say “since I’m pulling the motor anyway, I’ll go ahead and install new,
high compression pistons and those lightened connecting rods.” Consider that your
tired engine may improve dramatically by rebuilding to stock (or near stock). There are
exceptions, such as the Spider 2000 fuel system, but for the most part these cars were
very nice performers in stock form, and some relatively inexpensive changes may meet
all of your needs.

80

Engine Maintenance + Modification

FIAT 124 Spider

11.1 Cylinder Head Improvements

We’ve discussed how the head works in previous sections. Let’s talk about the things
that impede the efficiency of your cylinder head and how to overcome these
performance-robbing issues. We will start by discussing some cylinder head
nomenclature then working backwards, from the late model smog heads down to the
early Spider heads.

11.1.1 Nomenclature

You may have heard the expressions “porting,” “polishing,” “matching,” and
“blueprinting.” These are all methods of optimizing the airflow through the cylinder
head. Keep in mind that the head is the top of a big air pump (the engine) and the more
efficiently air can pass through the pump the more performance you will get from the
vehicle.

A head that is ported, matched, or blueprinted has the port sizes on the intake and
exhaust manifolds match those on the cylinder head. In other words, the pipes leading
out of the cylinder head and the pipes leading into the head do not reduce or have
interference in between. The gasket mating the two engine parts has been cut, if
necessary, so that it does not baffle the airflow in between. The ports on the exhaust
side are matched as well. FIAT heads typically have no resistance between the ports
and the gaskets do not protrude into the airflow.

A polished head is one that has had the combustion chambers and ports polished so that
nothing in the aluminum may disturb airflow. Polishing to an extreme can be
counterproductive as it may eliminate some of the “swirl” that is good for combustion.
The good news is that the FIAT heads are usually very smooth and require little or no
polishing.

11.1.2 Head Specifics

We’ll work backwards from the late model heads to the early types, since the most
popular and effective swaps occur more frequently with the late model Spiders. The
Spider 2000 fuel injected head is very “clean.” The fuel injection system did not require
the myriad of pollution control devices found on the carbureted 2000 head. It is
essentially a straight head with good combustion chamber size and shape, and good port
sizes. If you are curious about the hoses and pipes all over the top of the head they are
all related to the fuel injection system and are not actually interfering with the
combustion chambers, ports or valves. Fuel injected heads have the same camshaft
profile as every other FIAT Spider.

The Spider 2000 carbureted head is an example of what FIAT did to meet EPA
regulations. Depending on where your car was sold (California, for example, had
different regulations than other states) it may have an EGR bypass that squishes the #1
combustion chamber, reed valves that run into the head and to an air pump, vacuum
ports on the intake manifold for various emissions control devices, and, as mentioned
earlier, a restrictive exhaust system mated to it. The head, intake, exhaust, and

81

Engine Maintenance + Modification

FIAT 124 Spider

carburetor are collectively regarded as “boat anchors” and are always candidates for
replacement. Simply replacing the carbureted 2000cc head with one from a 2000cc fuel
injected or 1756cc engine will provide some improvement in efficiency.

The Spider 1756 head began life as a clean head, nearly identical to the 2000 FI head
described above. The 1756 head has smaller combustion chambers than the 2000
heads but is otherwise the same casting. By 1978 they had adopted a camshaft-driven
air pump and several emission control valves on the intake manifold. Unlike the 2000
carbureted head the 1756 never had the EGR port squishing the combustion chamber
and with little work any of the 1756 heads are desirable. One of the Lancia heads, the
1976 Monte Carlo (Scorpion) head, has larger ports than the other model years. The
1756 intake manifold is also desirable for the ADL, ADF, ADFA, DFEV, and DMSA
carburetors.

The Spider 1592 head was designed for, and mated to, the 1592cc engine used on the
1973 model year only. It is not laden with any specific emission control devices and is
really a clean head. If your vehicle has the 1592 motor (many were replaced with
1756’s) and you wish to maintain originality then this is the only head you can use. It is
otherwise not desirable for use on any other Spider.

The Spider 1608 and 1438 heads are clean heads with few or no emissions control or
other power-sucking devices added to them. They are slightly different that the later
series heads and, for the purposes of interchangeability (as described below), should
probably be kept on the engine they were designed for.

11.1.4 Interchangeability

The interchangeability of cylinder heads between the 1756 and 2000 Spiders is a true,
do-it-yourself, instant improvement. A clean 1756 head installed on top of the 2000
block (carbureted or fuel injected) results in a compression increase. Although not as
dramatic as the installation of high compression pistons, this can be done without pulling
the engine and requires the same amount of work as replacing the head gasket. The
difference being when the head gasket goes on the new head goes on top.

The 2000 FI head can also be installed on the 2000 carbureted engine. It will not alter
the compression ratio but will improve performance just by nature of a better, cleaner
design.

Other model years can be interchanged as well. The 1438 head is somewhat restrictive
and, with some minor welding on one of the coolant ports, can be replaced with the
1608 head. Experience has shown that most owners of these older Spiders are not
doing these upgrades as the performance gain is minimal. More suitable is the
installation of high compression pistons or other engine upgrades.

82

Engine Maintenance + Modification

FIAT 124 Spider

11.1.5 Camshafts

The camshafts installed on the 124 Spider are designed for normal road use. They
provide reasonable performance and are very durable. Other camshaft profiles are
available for the Spider, ranging from “street” to “hot street” to “racing.” If you are
considering camshaft replacement you should speak to people who have done this
before and understand the sacrifices of changing cams, such as:

• fuel economy may be reduced;

• idle and low speed operational quality may be reduced;

• acceleration may be undesirably jumpy; and,

• it may be impossible to pass emissions testing.

Understand that the camshaft is the engine’s brain. Changing that brain can result in a
very different engine. This operation may be very good or very poor for your conditions.
The stock cams are reliable, inexpensive, and do not significantly reduce street
performance. If you are considering camshaft changes visit someone with a modified
Spider and drive it, see if you like the overall operation.

It is important to check that your camshafts are in good operating condition and are not
worn. Measure or have the camshafts measured to the spec in your shop manual and, if
necessary, replace them. Stock and aftermarket camshafts are available from parts
vendors.

If you are new to the 124 Spider or just now considering engine changes, there are
stories all over the internet about the European specification 1608 camshaft having a
“better” profile than the later years. A few years ago Allen Lofland, a FIAT and Lancia
owner, led a crusade to prove this myth. Several people (myself included) bought
camshafts from the European 1608 Spiders. I bought my set right out of a car while
living in Europe – so I’m fairly certain of the originality. The cams were studied,
measured, inverted, turned, shaken, installed, driven, and…you probably guessed
already – it is a myth. The only notable difference in the USA and European 1608 Spider
was the installation of one (USA) or two (Europe) carburetors. Certainly there is room for
error, and these mythical camshafts may have existed, but we couldn’t find any.

11.1.6 Camshaft Wheels

The cast iron camshaft wheels are extremely durable but very heavy. Heavy engine
components will rob some power from the motor. Some of the camshaft wheels are
made of industrial-grade plastic, very light but lacked durability. In both cases there is
room for improvement. Later model FIAT wheels are slightly lighter as they have a hub­and-spoke construction (they are still iron). Aftermarket wheels can be had in very
lightweight aluminum.

83

Engine Maintenance + Modification

FIAT 124 Spider

Another option is adjustable camshaft wheels. These allow you to independently change
the timing of each camshaft to match your requirements. This compensation allows for
fine tuning of your engine to a degree not possible with stock components. Some of
these wheels require modification of the cylinder head; check with your supplier.
Adjustable camshaft wheels will add something new to your engine – complexity.
Consider that factor and speak to people who use them before installation.

11.1.7 Big Valves

Many suppliers sell big valves and/or peformance heads (meaning a stock head that has
been cut to fit big valves and ported for better airflow). Simply buying the big valves and
cutting the head to accommodate them or buying a performance head will not result in
any huge performance increase. The fuel delivery system has to be capable of bringing
more air and fuel into the combustion chamber. Big valve heads that are ported and
matched to a ported intake manifold will allow more air and fuel into the engine. A larger
carburetor will also be required on most engines.

11.2 Intake Manifolds

A variety of intake manifolds were installed on the carbureted Spiders. They followed
two basic designs as described earlier in this book, dual-plane and single-plane. To
recap, a dual plane manifold has two chambers inside of it, one is small and the other is
large. The larger one is the primary plenum and services the main throttle of the
carburetor. The smaller one is the secondary plenum and services the secondary
throttle. Dual plane manifolds are designed for optimal operation of the secondary
throttle of pneumatically-operated carburetors. Single-plane manifolds have one interior
space. Fuel and air from both throttles is delivered from this one large space into the
intake runners and then the combustion chambers.

With the exception of the 2000 series all of the manifolds are quite good. On the 2000
Spider the intake manifold should be used with the ADHA (stock) carburetor only. The
casting is such that the secondary throttle opening is too small for any other carburetor.
For pneumatic carburetors fitted to the earlier Spiders you should plan to use the stock
manifold for the model year and carburetor, for example, use the 1608/1592 manifold
with the 28/36 DHSA carburetor.

In all cases it is realistic to block off all of the ports except for the brake booster inlet.
Keep in mind that if you plan to keep emissions control devices that rely on manifold
pressure you can’t block off their ports.

11.3 Ignition

Running with points? There are a few decisions that need to be made about your
ignition system if you are looking to improve things. Improvement can often be made by
simply making sure your entire ignition system is working properly. Thad Kirk, a long
time respected FIAT owner, has articles on points ignitions on www.mirafiori.com

. He

notes that a well tuned points distributor provides reliability and performance right up

84

Engine Maintenance + Modification

FIAT 124 Spider

there with the electronic system. The trade-off is the older types require more
maintenance. If you want to eliminate this maintenance at the sacrifice of originality, you
have options.

The 1979-1985 electronic ignition system is a popular and easy upgrade from all previous
types (dual and single points). Installation of the late model system is straightforward,
you’ll need the distributor body (preferably rebuilt fully) in proper operating condition, and
the coil pack. The system directly replaces the old components and is tuned in the same
manner. There is an economic downside to the electronic ignition system conversion; to
make it work properly you must have a carburetor ported above the throttle plates. The
stock carburetors with this option are the 32 ADFA and the 28/32 ADHA; the aftermarket
carburetors are the 34 ADF, 36 ADL, 38 ADL, and 32/36 DFEV.

Figure 47: Location of port for vacuum advance

The figure of the ADFA carburetor above shows the location of the vacuum port, on the
main carburetor body above the throttle mechanisms. Unlike earlier models these
carburetors have a two piece construction and this port is tapped into the base of the
upper portion, just above the mixture screw. Without this connection the vehicle ignition
will not work properly and performance will degrade below that of the mechanical
system you’ve replaced.

The Marelliplex electronic ignition system is an option for those of us who do not want
to find ported vacuum. Marelliplex units are available as block-mounted (for 1438cc
motors) and cam-box mounted (for all other motors). Unfortunately, the cam-box mount
type is nearly impossible to find and will typically cost more than a new carburetor. The
block-mount is more common and shared with the Lancia beta, but will only fit well on
the 1438cc and 1608cc motors. There are manifolds for the 1756cc with a slight
indentation that will allow the distributor to fit the other motors, but the difficulty of

85

Engine Maintenance + Modification

FIAT 124 Spider

installation (it is almost too tight to tune) may make this undesirable. The block-mount is
available new from some parts vendors.

Another option is an optical trigger unit, available from most auto parts stores. These
units remove the wearable points in the distributor body. The most popular is the Crane
Fireball, sold by many parts vendors. If you are considering one of these units you
should speak with other owners on installation specifics, ease of use, and reliability.

11.4 Exhaust and Emissions Control

There are few options in the exhaust improvement category. There are the stock
systems that have a four-two-one design, and aftermarket systems of similar design.
Unless you have a specific need for an aftermarket design, the FIAT 4-2-1 is efficient,
well designed, fits correctly (unlike many aftermarket systems), and has a stock look.
For carbureted engines made after 1973 the 4-2-1 type used on the 1756cc Spiders will
work well. The 4-2-1 type used on the 2000cc Fuel Injected spider will work on these
models as well (although it may hang a little low for 1756cc Spiders).

If you use the fuel injected 4-2-1 exhaust on a carbureted engine note that you will need
to block off the oxygen sensor port and, unless you intend to use the catalytic converter
and rear section from a fuel injected car, modify the flange under the vehicle for use with
the carbureted, 3-bolt catalytic converter. A “full conversion” to the FI 4-2-1 is actually
quite easy and saves the hassle of having to cut, weld, or alter the stock components.

The emissions control devices installed on your Spider are probably inoperable. The
parts to service these devices are also few and far between. In some cases the
pollution control equipment operates so poorly that it can increase emissions. If you are
concerned about emissions then it may interest you to note that EPA mandated these
devices be installed regardless of whether the engine was within good air quality ranges
to begin with. An in-tune Spider engine without modifications to the fuel delivery
system is a very clean burning engine; even without a catalytic converter many will pass
all but the visual inspection of the vehicle.

There are some emissions control devices that you should probably keep. The charcoal
canister, which is designed to absorb the stink of raw fuel, is good to have functioning
correctly. It can be “recharged” by simply cutting it open and refilling with activated
charcoal (from a fish store). They can also be bought new from numerous sources as
the FIAT part was used on various years of other European cars well through the 1990’s.
The catalytic converter is another part you might consider leaving intact. Although it
certainly consumes some power (it creates backpressure by its very design), newer
types are far less restrictive than the original equipment FIAT types.

Keep in mind that some states have laws around smog checks and original equipment.
Cars made after a certain year may need to pass emissions tests and visual inspection s
to verify that all of the original equipment is in place and working.

86

Engine Maintenance + Modification

FIAT 124 Spider

11.5 Carburetors

We discussed the stock carburetors earlier in this book. The carburetors were
reasonably good matches to the engine size; however, a general rule is that the cars
were always slightly under-carbureted. Every time an owner installs a DHSA2 on a car
previously fitted with the DHSA1 the performance increases. Simply put, the DHSA2
allows more air into the motor. Every Spider 2000 owner who replaced the ADHA and
manifold with a DFEV, ADF, or ADFA has felt his car spring to life. This section deals
with good swaps and good new carburetors to install on your car.

Most folks who are considering a carburetor swap will likely stay away from the
pneumatic carburetors. Truth be told they aren’t as fun to drive; the secondary always
lags behind the first regardless of how hard you press the gas pedal. They were
designed to deliver the secondary fuel at an “appropriate” time, which is fine for fuel
economy and emissions, but not so much for overall driving fun. The pneumatic
carburetors are harder to find parts for and their unpopularity in modern applications
makes parts availability scarcer every day.

Mechanical carburetor swaps are very easy on the Spiders. The easiest and most
popular is done by owners of the Spider 2000. The Spider 2000 owner can buy an 1756
intake manifold and the Weber 32ADFA carburetor and install them in the same locations
as the old carburetor. Plug in the fuel lines, distributor vacuum pulse line, cold start
hoses, and linkages, and get an immediate performance increase. The two carburetors
are externally near identical, meaning that the hoses and other pieces line up nicely. The
real gain for the Spider 1756 and 2000 owner is from the other Weber ADF, the 34 ADF.
Available new from most parts vendors the 34 is a very large and powerful carburetor
with no unnecessary components. It has connections for the distributor vacuum and
vapor recovery; otherwise it is just a fine Weber carburetor that adds instant fun to the
2000cc vehicles. The 34 ADF should always be mounted on the 1756 ADFA manifold.

If it fits your budget, consider the following combinations:

Table 11: Engine Component Combinations

Block and Head Intake Manifold Exhaust System Recommended Carburetor

2000cc
2000 FI Cylinder Head
Stock Pistons

2000cc
1756 Cylinder Head
Stock Pistons

1756cc 2000cc FI 4-2-1 Weber 34 ADF

1756cc 1756cc 4-2-1

or
2000cc FI 4-2-1

or
Weber 28/36 DFEV

Weber 34 ADF
or
Weber 28/36 DFEV
or
Weber 36 ADL

87

Engine Maintenance + Modification

Block and Head Intake Manifold Exhaust System Recommended Carburetor

FIAT 124 Spider

2000cc
1756 Cylinder Head

8.9:1 or 9.1:1 Pistons

2000cc
1756 Cylinder Head

8.9:1 or 9.1:1 Pistons
Mild Camshafts (40/80)

1756cc
1756 Cylinder Head
Stock Camshafts
Electronic Ignition

1756cc
1756 Cylinder Head
Mild Camshafts (40/80)
Electronic Ignition

1608cc
1608 Cylinder Head
Stock Camshafts
Electronic Ignition

1756cc

1756cc

1756cc 1756cc 4-2-1 Weber 32 ADF

1756cc 1756cc 4-2-1 Weber 34 ADF

1756cc or Dual IDF 1608cc 4-2-1 Weber 34 DMS

1756cc 4-2-1
or
2000cc FI 4-2-1

1756cc 4-2-1
or
2000cc FI 4-2-1

Weber 34 ADF
or
Weber 28/36 DFEV
or
Weber 36 ADL

Weber 34 ADF
or
Weber 28/36 DFEV
or
Weber 36 ADL
or
Weber 38 ADL

or
Weber 34 ADF

or
Weber 28/36 DFEV

or
Weber 34 ADF
or
Dual IDF

1608cc
1608 Cylinder Head
Mild Camshafts (40/80)
Electronic Ignition

1608cc
1608 Cylinder Head
Aggressive Camshafts (42/82)
Electronic Ignition

1438cc
1438cc Cylinder Head
High Compression Pistons
Electronic Ignition

1438cc
No other modifications

1756cc or Dual IDF 1608 4-2-1 Weber 34 DMS

1756cc or Dual IDF 1608 4-2-1 Weber 34 ADF

1438cc 1438 Weber 34 DMS

1438cc 1438 Weber 28/36 DHSA 2

or
Weber 34 ADF
or
Dual IDF

or
Dual IDF
or
Weber 36 ADL

or
Weber 28/36 DHSA2

88

Engine Maintenance + Modification

Figures

Figure 1: Engine Identification 9
Figure 2: Updraft Carburetor. 11
Figure 3: Air Bleed Correction. 12
Figure 4: Idle Speed Circuit. 13
Figure 5: Transition Stage. 14
Figure 6: Diaphragm-type accelerating pump 15
Figure 7: Offset choke 16
Figure 8: Mechanically controlled differential opening of the throttles. 17
Figure 9: Pneumatically controlled differential opening of the throttles 18
Figure 10: DHSA1 Carburetor Base Plate 19
Figure 11: DHSA 20
Figure 12: DHSA External Parts, Float Mechanisms, and Choke Assembly 21
Figure 13: DHSA Jetting, Throttle Mechanisms, and Internal Parts 21
Figure 14: Weber 40 IDF Carburetor Side View 22
Figure 15: IDF Normal Operation 22
Figure 16: IDF Progression 23
Figure 17: IDF Acceleration 24
Figure 18: IDF Cold Start Devices 24
Figure 19: IDF Dimensions 25
Figure 20: DMS Carburetor Side View 26
Figure 21: DMS Normal Operation 26
Figure 22: DMS Progression 27
Figure 23: DMS Acceleration 28
Figure 24: DMS Starting 29
Figure 25: DMS Dimensions 30
Figure 26: ADF Carburetor Side View 30
Figure 27: ADF Normal Operation 31
Figure 28: ADF Idle Speed and Progression 32
Figure 29: ADF Acceleration 32
Figure 30: ADF Starting 33
Figure 31: ADF Anti-Pollution Device 34
Figure 32: ADF Dimensions 35
Figure 33: Bosch L-Jetronic Fuel Injection as used in the FIAT Spider 2000. 39
Figure 34: Cold Start Operation in the Bosch L-Jetronic System 41
Figure 35: Warm-up Operation in the Bosch L-Jetronic System 42
Figure 36: Idle Speed Control in the Bosch L-Jetronic System 43
Figure 37: Idle speed controls on the Spider 2000 49
Figure 38: Primary Connections on the Electronic Control Unit 50
Figure 39: Primary Fuel Injection Circuits 51
Figure 40: Fuel Injection System Electrical Diagram 52
Figure 41.1: Intake 60
Figure 41.2: Compression 60
Figure 41.3: Ignition 60
Figure 41.4: Exhaust 60
Figure 42: Initial Ignition Setting 69
Figure 43: Final Timing (2000cc engine) 70

FIAT 124 Spider

89

Ta b l e s

Table 1: Engine Identification Table 10
Table 2: Carburetor Identification 19
Table 3: Major Fuel Injection System Components 45
Table 4: Fuel Injection System Part Number Reference 53
Table 5: Fuel Injection System Troubleshooting 56
Table 6: Cylinder Head Casting Number Table 61
Table 7: Intake Manifold Casting Numbers 63
Table 8: Exhaust System Casting Numbers 65
Table 9: Ignition System Components 68
Table 10: Ignition Advance by Engine Type 70
Table 11: Engine Component Combinations 87

Engine Maintenance + Modification

FIAT 124 Spider

90

www.artigue.com/fiat

Copy