Traxxas 4810, Nitro 4-Tec 4810 Owner's Manual

Nitro 4-Tec

Owner

’

s

Manual

Model

4810

Traxxas Corporation
Corporate Headquarters
1100 Klein Road
Plano,Texas 75074
Phone: [phone]
Toll-free 1-888-TRAXXAS

Traxxas U.K.
P. O. Box 1128
Winterbourne, Bristol BS17-2SH
England
Phone: [phone]

Internet
www.Traxxas.com
E-mail: [e-mail]

Entire contents ©2003 Traxxas Corporation. Traxxas, Nitro 4-Tec,
TRX 2.5, TQ, Top Fuel,EZ-Start, Ready-To-Race, and ProGraphix
are trademarks or registered trademarks of Traxxas Corporation.
Other brand names and marks are the property of their
respective holders and are used only for purposes of
identification. No part of this manual may be reproduced or
distributed in print or electronic media without the express
written permission of Traxxas.

020926

2

Thank you for purchasing the Traxxas Nitro 4-Tec.This manual
contains the instructions you will need to operate, and maintain
your Nitro 4-Tec. Look over the manual and examine the Nitro
4-Tec carefully before running it. If for some reason you think
the Nitro 4-Tec is not what you wanted, then do not continue
any further.Your hobby dealer absolutely cannot accept a Nitro
4-Tec for return or exchange after it has been run.

The Nitro 4-Tec’s new TRX 2.5 Racing Engine™ is the most
powerful engine of its size ever available in a Ready-To-Run car.
Two years of engineering development, advanced design, and
thousands of hours of testing put the TRX 2.5 in a class by itself.
Each part of the TRX 2.5 - from the air filter on the slide
carburetor,to the tip on the dyno-tuned exhaust system - has
been carefully engineered to provide maximum power over the
broadest RPM range.

Traxxas was the first with standard on-board electric starting.
The new second generation EZ-Start has evolved into an
incredibly advanced and reliable starting solution, featuring
thermal protection for the motor and built-in diagnostics to
monitor the condition of the glow plug.
In this manual, we’ll take you step-by-step through all necessary
set-up, break-in, tuning,and operating procedures. Even if you

are an experienced R/C enthusiast,it is important for you to
read and follow the procedures in this manual.Pay
particular attention to the fuel requirements and break-in
procedures. The advanced design of the TRX 2.5 racing

engine does not follow traditional old-fashioned thinking
regarding fuel and break-in procedures.

4 Before You Proceed

5 Safety Precautions

6 Tools, Supplies

and Required
Equipment

7 Anatomy of the

Nitro 4-Tec

8 Quick Start: Getting

Up to Speed

9 Decorating Your

Nitro 4-Tec Body

10 Installing Your

Nitro 4-Tec Body

11 The Traxxas TQ

Radio System

21 The TRX 2.5

racing engine

37 Driving the Nitro

4-Tec

38 Adjusting

Your Nitro 4-Tec

42 Trouble Shooting

Your Nitro 4-Tec

44 Maintaining

and Storing
Your Nitro 4-Tec

45 Index

3

Introduction

Before You Proceed

Carefully read and follow all instructions in this and any
accompanying materials to prevent serious damage to your
Nitro 4-Tec.Failure to follow these instructions will be
considered abuse and/or neglect.

Before running your Nitro 4-Tec, look over this entire manual,
and examine the car carefully.If for some reason you decide the
Nitro 4-Tec is not what you wanted, then do not continue any
further. Your hobby dealer absolutely cannot accept a Nitro

4-Tec for return or exchange after it has been run.

Warnings, helpful hints, and cross-references

Throughout this manual, you’ll notice warnings and helpful
hints, identified by the icons below. Be sure to read them!

An important warning about personal safety or avoiding
damage to your Nitro 4-Tec and related components.

Special advice from Traxxas to make things easier and
more fun.

Refers you to a page with a related topic.

Support

If you have any questions about your Nitro 4-Tec or its
operation, call the Traxxas Technical Support line toll-free at:
1-888-TRAXXAS (1-888-872-9927)

Technical support is available Monday through Friday from 8:30
am to 9:00pm central time. Technical assistance is also available
at www.Traxxas.com.You may also e-mail customer support
with your question at [e-mail] thousands of
Traxxas R/C enthusiasts in our online community at
www.ReadyToRun.org

Traxxas offers a full-service, on-site repair facility to handle any
of your Traxxas service needs. Maintenance and replacement
parts may be purchased directly from Traxxas, or you can save
shipping and handling costs by purchasing them from your
local hobby dealer.

4

All of us at Traxxas want you to safely enjoy your new Nitro
4-Tec.Operate your Nitro 4-Tec sensibly and with care, and it will
be exciting, safe, and fun for you and those around you. Failure
to operate your Nitro 4-Tec in a safe and responsible manner
may result in property damage and serious injury.The
precautions outlined in this manual should be strictly followed
to help ensure safe operation. You alone must see that the
instructions are followed and the precautions are adhered to.

Important Points to Remember

R/C fuel is dangerous and highly poisonous. Always follow all
directions and precautions printed on the fuel container.

R/C fuel, especially when in a fuel dispensing bottle, may
look like a cool drink to a child. Keep all fuel out of the reach
of children at all times. Do not place fuel containers on the
ground where children can get to them while you are
driving.

R/C fuel is flammable. Never allow smoking, sparks,heat or
flame in the presence of fuel or fuel vapors.

The engine and exhaust system may become extremely hot
during use. Be careful not to touch the parts, especially when
refueling or stopping the engine.

Prolonged exposure to the engine exhaust can be harmful.
Avoid breathing the engine exhaust. Always run your Nitro
4-Tec outdoors, in a well-ventilated area. Never run the
engine indoors.

Don’t operate your Nitro 4-Tec at night, or anytime your line of
sight to the model may be obstructed or impaired in any way.

Never operate your Nitro 4-Tec in crowds of people or busy
pedestrian areas.The Nitro 4-Tec is extremely fast,and may
cause injury to those unaware of its presence.

Because the Nitro 4-Tec is controlled by radio, it is subject to
radio interference from many sources beyond your control.
Since radio interference can cause momentary loss of
control, always allow a safety margin in all directions around
your model to prevent collisions.

The engine can be loud. If the noise makes you
uncomfortable, wear ear protection. Be considerate of your
neighbors by not running your model early in the morning
or late in the evening.

Most importantly, use good common sense at all times.

▼▼ ▼▼

▼▼▼▼ ▼▼

All instructions
and precautions

outlined in this
manual should be strictly
followed to ensure safe
operation of your Nitro
4-Tec.

The Nitro 4-Tec is

not intended for

use by those under
16 years of age without
the supervision of a
responsible and
knowledgeable adult.

5

Safety Precautions

Tools, Supplies, and Required Equipment

Your Nitro 4-Tec comes with a set of specialty metric tools. You’ll
need to purchase other items, available from your hobby dealer,
to operate and maintain your model.

For more info on
batteries, see Use

the Right Batteries

on page 13.

A peak-detecting
charger is

recommended for
best performance and
longest battery life. For
more information, see
Use the Right Charger on
page 30.

12 AA alkaline batteries for the radio system

7.2-volt NiCad battery pack for the
EZ-Start starting system

NiCad battery charger

Traxxas Top Fuel™

10% quart - #5010 • 20% quart - #5020
10% gallon - #5060 • 20% gallon- #5070

Fuel dispensing bottle (Traxxas part #5001)

TR

AXXAS

1.5mm hex wrench

2.0mm hex wrench

Glow plug (universal) wrench

Turnbuckle wrenches

Batteries

Fuel

Supplied Tools

Your Nitro 4-Tec comes with these specialty metric tools:

Other Required Tools and Supplies

Safety glasses

#2 Phillips screwdriver

After-run oil (WD-40™) to protect
the engine from corrosion

#1 Phillips screwdriver

Small flat-blade screwdriver (1/8 inch blade)

Filter oil (for the foam air filter)

see page 27 for details

Hobby knife

6

U-Joint wrench

4-way wrench

Anatomy of the Nitro 4-Tec

Battery

Holder

Fuel

Tank

Fuel Tank

Lid

Steering

Servo

Suspension

Arm

Front Bumper

Plate

Shock

(Oil Damper)

Tie Rod

(Turnbuckle)

Throttle/Brake

Servo

Receiver

Bearing

Block

Air

Filter

Pipe

Header

Engine

see pg.21 for details

Pressure

Line

Fuel
Line

EZ-Start

Motor

EZ-Start

Plug

Shock
Tow e r

Body/Foam

Bumper Mount

Chassis
(lower)

7

On/Off
Switch

Antenna

Mount

Pipe

Hanger

Front Camber Link

(Turnbuckle)

Racing

Tires

Two-Speed

Transmission

Bellcrank

Steering

Front

Differential

Front

Drive Belt

Drive Belt

Pulley

Rear

Differential

Body

Mount

Center

Drive Belt

The following guide is an overview of the

procedures for getting your Nitro 4-Tec running,
from opening the box to breaking in and tuning your engine.
Refer to the pages indicated for details on each step.Look for the
Quick Start logo on the bottom corners of Quick Start pages.

1. Charge the battery pack • See sidebar, page 30

The EZ-Start requires a fully charged 7.2-volt
battery pack (not included).

2. Get the right fuel • See page 26

Use Traxxas Top Fuel™ or consult with Traxxas
before using other fuels.

3. Install the antenna • See page 15

Install the antenna mast in the Nitro 4-Tec.

4. Decal the body • See page 9

You will need to use the body during the break-in
process so it’s best to decal it before you use it on
the car.

5. Install the body mounts • See page 10

Install the body mounts and foam bumper.

6. Install batteries in the transmitter • See page 13

The Nitro 4-Tec requires 8 AA alkaline or rechargeable
batteries for the transmitter.

7. Install batteries in the model • See page 14

The Nitro 4-Tec requires 4 AA alkaline or rechargeable
batteries for the receiver.

8. Install the EZ-Start battery • See page 30

Install and connect the 7.2-volt battery pack in
the EZ-Start controller.

9. Turn on the radio system • See page 18

Make a habit of turning the transmitter on first, and off last.

10. Check servo operation • See page 19

Make sure the throttle and steering servos are working
correctly.

11. Range test the radio system • See page 20

Follow this procedure to make sure your radio system
works properly at a distance and that there is no
interference from outside sources.

12. Fill the fuel tank • See page 26

Use your fuel-dispensing bottle to fill the tank.

13. Connect the EZ-Start to the model • See page 31

Learn the proper way to use the EZ-Start electric
starting system

14. Start the engine • See page 32

Learn to use the correct starting procedure for your TRX 2.5.

15. Break-in your engine • See page 32

Follow the break-in instructions exactly to ensure the best­performing, longest-lasting engine.

16. Tune your engine • See page 34

Learn how to set the fuel mixture needles for optimum
engine performance.

17. Drive your Nitro 4-Tec • See page 37

Driving tips and adjustments for your Nitro 4-Tec

18. Maintaining your Nitro 4-Tec • See page 44

Follow these critical steps to maintain the performance
of your Nitro 4-Tec and keep it in excellent running
condition.

The Quick Start
Guide is not

intended to
replace the full operating
instructions available in
this manual. Please read
this entire manual for
complete instructions
on the proper use and
maintenance of
your Nitro 4-Tec.

Quick Start: Getting up to Speed

8

Decorating Your Nitro 4-Tec Body

9

Applying The Decals

The ProGraphix painted
body is covered with a
protective film for shipping.
You must remove this film
before applying any decals.

To remove the film, lift a
corner of the film and
carefully pull it off the body
in one continuous piece.

Your Nitro 4-Tec decals are
die-cut for easy removal. Use
a hobby knife to lift the
corner of a decal and lift it
from the backing.

Carefully position the decal
over the desired location
and press one side on the
body.Pull the decal tight
and use a finger to gradually
smooth out any air bubbles
as you apply the decal.

Look at the photos on the box for typical decal placement.

Installing Body Mounts

The body mount parts are located in a separate bag with your
instructions. The front body mount posts attach to the front
bumper with 3x10mm counter-sunk self-tapping screws. Now
slide the foam bumper over the front mounts,as shown in the
drawing.The excess length of the mounts should be trimmed
off after the body is installed.The rear body mounts attach as
shown in the drawing.

10

Installing Nitro 4-Tec Body Mounts

3x10mm Countersunk
Self-tapping screws

Foam
Bumper

3x14mm Washerhead
Self-tapping screws

Installing Rear
Body Mounts

Installing Front
Body Mounts

11

The Traxxas TQ Radio System

Your Nitro 4-Tec (model 4810) is equipped with the TQ Radio
System.The TQ is a 2-channel system that provides high-power
output up to a quarter mile and control for two servos. The Nitro
4-Tec makes use of two channels for throttle/brake and steering.

Nitro 4-Tec Wiring
Diagram

Antenna

On/Off
Switch

Black
Negative

Red
Positive

Receiver

4-Cell

Battery Holder

Channel 1

Steering Servo

Channel 2

Throttle Servo

Channel 2
Channel 1

Battery

C

H

.2

C

H

.1

Antenna

Throttle Neutral Adjust

Steering Wheel

Throttle Trim

Steering Trim

Power Switch

Power Indicator

Battery Compartment

Servo
Reversing
Switches

Throttle Trigger

Radio System Terminology

Please take a moment to familiarize yourself with these radio­system terms.They will be used throughout this manual.

Channel - The 27 MHz frequency band is divided into 6 channels

so that up to six models can be operated simultaneously.Each
channel is referred to by its flag color and channel number,as
shown below.

Clearing your frequency - A routine, verbal check to make sure

nobody else in your area is operating on the same channel.
Always clear your frequency by calling out your channel
number before operating your model.Wait or move to
another area if your channel is already being used.

Crystal (X-tal) - The plug-in device that determines which

channel the radio system will operate on. For each channel,
there are two crystals, one for the receiver and one for the
transmitter.Of those two crystals, the one marked with the
lower number (.455 MHz lower) must be inserted into the
receiver.

Frequency band - The radio frequency used by the transmitter

to send signals to your Nitro 4-Tec.All Traxxas RTR models
operate on a 27 MHz frequency band.

Neutral position - The standing position that the servos seek

when the transmitter controls are at the neutral setting.

NiCad - Refers to rechargeable, nickel-cadmium batteries. The

most economical choice, since they may be recharged up to
500 times.

Receiver - The radio unit inside your Nitro 4-Tec that receives

signals from the transmitter and relays them to the servos.

Servos - Small motor units in your Nitro 4-Tec that operate the

throttle and steering mechanisms.

Two-channel radio system - The TQ radio system,consisting of

the receiver, the transmitter, and the servos.The system uses
two channels: one to operate the throttle, one to operate the
steering.

Transmitter - The hand-held radio unit that sends throttle and

steering instructions to your Nitro 4-Tec.

Tri m - The fine-tuning adjustment of the neutral position of the

servos, made by turning the throttle and steering trim knobs
on the face of the transmitter.

Channel Frequency Band Flag Color Traxxas Part No.

1 26.995 Brown 2031

2 27.045 Red 2032

3 27.095 Orange 2033

4 27.145 Yellow 2034

5 27.195 Green 2035

6 27.255 Blue 2036

Learn terms related

to the TRX 2.5

racing engine

beginning on page 23.

The Traxxas TQ Radio System

12

13

The Traxxas TQ Radio System

Installing Transmitter Batteries

Your TQ transmitter uses 8 AA batteries. The battery
compartment is located at the base of the transmitter.

1. Remove the battery compartment door by pressing the
tab and lifting the door up.

2. Install the batteries in the correct orientation as indicated
in the battery compartment.

3. Reinstall the battery door and snap it closed.

4. Turn on the transmitter and check the power indicator for

a solid red light.

If the power indicator light flashes, then the transmitter
batteries are weak, discharged or possibly installed incorrectly.
Replace with new or freshly charged batteries.The power
indicator light does not indicate the charge level of the
receiver batteries in the model.

Use the Right Batteries

Your transmitter and receiver
use AA batteries. Use new
alkaline batteries, or
rechargeable batteries such as
NiCad or Ni-MH (nickel-metal
hydride) batteries in your
transmitter and receiver. Make
sure rechargeable batteries are
fully charged according to the
manufacturer’s instructions.

If you use rechargeable
batteries in your transmitter, be
aware that when they begin to
lose their charge, they lose
power much more quickly than
regular alkaline batteries.

Caution: Discontinue running
your Nitro 4-Tec at the first
sign of weak batteries
(flashing red light) to avoid
losing control.

If the power indicator
doesn’t light red, check

the polarity of the
batteries. Check rechargeable
batteries for a full charge.

CH.2

CH.1

Installing Receiver Batteries

The radio receiver in your Nitro 4-Tec uses 4 AA batteries. The
receiver battery holder is located underneath the top plate, just
to the right of the fuel tank.

1. Press the tab on the reusable zip tie to release the
battery holder.

2. Remove the battery holder
and install 4 AA alkaline
batteries. Make careful note
of the battery polarity by
comparing against the
diagrams in the battery
holder.

3. Stretch a rubber balloon
over the battery holder to
prevent fuel contamination.

4. Install the battery holder
into the car and secure it to
the top plate with the
reusable zip-tie. Make sure
the battery holder is secure
in the model and will not
come loose. If the tie wrap is
loose, it will interfere with
the middle drive belt.

If you use
rechargeable
batteries in your

receiver, be aware that
when they begin to lose
their charge, they lose
power much more quickly
than regular alkaline
batteries. Signs of weak
receiver batteries include
sluggish steering response
and shortened radio range.
Caution: Discontinue
running your Nitro 4-Tec at
the first sign of weak
batteries to avoid losing
control.

If the radio system
doesn’t appear to
work when the

transmitter and receiver
switches are turned on,
check for correct battery
installation.

The Traxxas TQ Radio System

14

4-cell
battery
holder

The Traxxas TQ Radio System

15

Spray a little window
cleaner on the

antenna wire to
make it easier to push
through the antenna tube.

Don’t shorten the

length of the

antenna wire. Its
length is tuned to the
frequency band; cutting it
could severely shorten the
radio system’s range.

Don’t push the

transmitter antenna

down from the top.
Pull it down from the
bottom, one segment at a
time, to prevent binding and
kinking the antenna mast.

Setting Up the Antenna

You must install the antenna mast (tube) before you operate
your Nitro 4-Tec.You’ll find the plastic antenna tube and tip in
the bag with your manuals and documentation.

1. Locate the black antenna wire that exits the receiver. The
Nitro 4-Tec receiver is mounted on the side of the upper
chassis.The receiver is wrapped in a balloon for protection.
The color of the balloon indicates the channel number (see
page 12).

2. Pull the wire straight with your fingers and then insert the
end of the wire into one end of the antenna tube. Push the
wire all the way through the antenna tube.

3. Pull the remaining wire through the antenna tube, and then
insert the base of the antenna tube into the molded post on
top of the chassis.

4. Fold the remaining antenna wire over the top of the tube
and secure it with the antenna tip.

5. On the transmitter, always fully extend the telescoping
antenna when running your Nitro 4-Tec. Make a habit
of holding the transmitter so that the antenna points
straight up.

Antenna Tip

Antenna Tube

The Traxxas TQ Radio System

C

H

.2

C

H

.1

TQ Radio System Controls

16

Other TQ Radio System Adjustments

In addition to the electronic throttle and steering trim controls,
your radio system features throttle neutral adjustment and
servo reversing switches.

Throttle Neutral Adjustment

The throttle neutral adjustment is located on the transmitter
face and controls the forward/brake travel of the throttle
trigger. Change the adjustment by pressing the button and
sliding it to the desired position.There are two settings
available:

50/50: Allows equal travel for both acceleration and braking.

70/30: Allows more throttle travel (70%) and less

brake travel (30%).

50/50 is the required setting for the Nitro 4-Tec with
the TRX 2.5 Racing Engine.

Electronic Throttle Trim

The electronic throttle trim located on the face of the
transmitter adjusts the neutral (center) point of the throttle
servo when the servo is at rest. This control has been preset for
you at the factory. If necessary, adjust the control so that the
carburetor is at idle, and the brakes are not applied (the model

▼▼

The Traxxas TQ Radio System

17

will roll freely). Once the engine is running, do not use the
throttle trim to raise or lower the engine idle speed. Make the
idle speed adjustment on the carburetor.

Electronic Steering Trim

The electronic steering trim located on the face of the
transmitter adjusts the neutral (center) point of the steering
servo when the servo is at rest. Adjust this control to make the
model drive straight with no steering input at the wheel.

Servo Reversing Switches

The servo reversing switches are located on the front of the
transmitter,next to the on/off switch. Moving a switch reverses
the direction of the corresponding servo.

Each switch corresponds to a channel, as shown below. For
example, if you turn the steering wheel to the right and your
front wheels turn left, you would move the channel 1 switch to
correct the servo direction. It may be necessary to adjust the
corresponding trim control after moving a switch.

CH.2

CH.1

Channel Servo

1Steering
2Throttle and braking

TQ Radio System Rules

Each time you prepare to run your Nitro
4-Tec,you must clear your frequency to
be sure no one else in the area is using
the same channel as you.

There are six possible channels,
numbered 1 through 6. Each is
represented by a color. Look at the
crystal plugged into the back of your
transmitter to determine which channel
your car is assigned to.

Always turn your TQ transmitter on first and off last. This
procedure will help to prevent your Nitro 4-Tec from
receiving stray signals from another transmitter, or other
source, and running out of control.

Always have the transmitter and receiver turned on before
you start the engine. Never turn the radio system off while
the engine is running.The on/off switch in the model only
turns the receiver on and off.It does not turn off the engine.

Always use new or freshly charged batteries for the radio
system. Weak batteries will limit the range of the radio signal
between the receiver and the transmitter. Loss of the radio
signal can cause you to lose control of your Nitro 4-Tec.

▼

▼▼ ▼

Channel 1

Brown

Channel 2

Red

Channel 3

Orange

Channel 4

Yellow

Channel 5

Green

Channel 6

Blue

C

H.2

C

H.1

1

23

Remember, always
turn the TQ

transmitter on first
and off last to avoid damage
to your Nitro 4-Tec.

18

The Traxxas TQ Radio System

The Traxxas TQ Radio System

Using the TQ Radio System

The TQ Radio System was pre-adjusted at the factory.The
adjustment should be checked, before running the model, in
case of movement during shipping. Here’s how:

1. Fully extend the chrome antenna mast on the transmitter

and turn the switch on.The red indicator light on the
transmitter should be solid red (not flashing).

2. Turn on the receiver switch in the model.The switch is

located on the rear shock tower.

3. Position the Nitro 4-Tec so that its front wheels are off the

ground.

4. Turn the steering wheel on the transmitter back and forth

and check for rapid operation of the steering servo. Also,
check that the steering mechanism is not loose or binding. If
the steering operates slowly,check for weak receiver
batteries.

5. When looking down at model,the front wheels should be

pointing straight ahead. If the wheels are turned slightly to

the left or right, slowly adjust the steering trim control on the
transmitter until they are pointing straight ahead.

6. Operate the throttle trigger on the transmitter and check for
rapid operation of the throttle servo.When the throttle
trigger is pulled back, the carburetor should open.When the
throttle trigger is pushed all the way forward, the brake
should lock.

7. Once adjustments are made, turn off the receiver on your
Nitro 4-Tec, followed by the hand-held transmitter.

Brake

Throttle/Brake

Servo

Throttle

0°0°

When the engine
is running, don’t

use the throttle
trim on the transmitter to
adjust the engine idle
speed. Instead, use the
idle speed adjustment on
the carburetor.

19

Steering

Servo

Nitro 4-Tec Servo
Operation

The Traxxas TQ Radio System

Range-Testing the TQ Radio System

Before each running session with your Nitro 4-Tec, you should
range-test your radio system to ensure that it operates properly.

1. Turn on the radio system and check its operation as
described in the previous section (Using Your Radio System,
pages 18- 19).

2. Have friend hold the model with the engine off.

3. Make sure your transmitter antenna is fully extended, and

then walk away from the model with the transmitter until you
reach the farthest distance you plan to operate the model.

4. Operate the controls on the transmitter once again to be sure
that the model responds correctly.

5. Do not attempt to operate the model if there is any problem
with the radio system or any external interference with your
radio signal at your location.

Don’t attempt to
operate your Nitro

4-Tec if there are
any problems with your
radio system or radio
interference at your
location.

20

Introduction

There’s nothing like the TRX 2.5 racing engine in your new Nitro
4-Tec.The TRX 2.5 racing engine is vastly superior to typical R/C
engines and belongs in the category of specialty high­performance racing engines. It’s the result of years of focused
engineering development, and thousands of hours of
controlled testing and rigorous real-world running.It offers
unprecedented power and performance that turns ready-to-run
into Ready-To-Race

®

.

The TRX 2.5 racing engine takes a total-system approach.Each
part of the engine, from the air filter to the exhaust tip, is
carefully engineered to work in harmony with other engine
components. Each part complements the next, to extract
maximum power.The TRX 2.5 is designed to be tolerant of
variations in tuning, and to run successfully through a wide
range of variable atmospheric conditions, such as changes in
temperature, humidity, and altitude.

The TRX 2.5 is manufactured to exacting tolerances and requires
a specially-designed break-in procedure to accomplish the final
precision fitting of the internal engine components. It is very
important that you follow the new break-in procedure as closely
as possible to achieve the best performance and longest life
from your TRX 2.5 racing engine.Old style break-in procedures,
such as simply running the engine with a very rich fuel mixture
for the first 4 tanks of fuel, will not achieve the best results.
Follow the steps in this manual.

A routine maintenance schedule is also required to keep the
TRX 2.5 in top running condition. Cleaning the air filter after
each hour of running is particularly important. Also it is
extremely important to perform after-run maintenance on the
engine to prevent corrosion of the internal engine components
(see page 44).

Traxxas strongly
discourages

changing or
modifying any part of the
TRX 2.5 racing engine. Old
tech tips and tricks that
may have boosted the
power of other engines
could seriously diminish the
performance of the TRX 2.5.

There’s more advanced
thinking, development and
testing in the stock parts of
your TRX 2.5 than in many
aftermarket manufacturer’s
so-called performance
parts. The TRX 2.5 is already
one of the most powerful
engines in its class and
simply will not benefit from
average, low-tech,
aftermarket bolt on
performance items.

The TRX 2.5 Racing Engine

21

The TRX 2.5 Racing Engine

TRX 2.5 Illustrated

Air

Filter

Head Protector

Head (Cylinder head)

EZ-Start

Drive Unit

EZ-Start

Motor

Low-Speed

Needle

Throttle

Arm

Clutch

Bell

Flywheel

Carburetor

Air Intake

Fuel Intake

High-Speed Needle

Idle Speed

Screw

EZ-Start

Plug

Positive

Wire

Negative

Wire

Fuel Line

Fuel Tank

Pipe

Exhaust

Tip

Pressure

Line

Ground

Wire

Glow Plug

Wire

EZ-Start

Controller

22

Crankshaft

Crankcase

Header

Pipe

Coupler

The TRX 2.5 Racing Engine

Terms to Know

You’ll find these Nitro R/C engine terms throughout this
section of the manual.

.15 - .15 or “15”refers to the size of the engine. The TRX 2.5 is .15

cubic inches or 2.5 cubic centimeters (cc).The name “TRX 2.5”
is derived from the cc measurement.

ABC - Abbreviation for aluminum, brass,and chrome. Refers to

engine construction that consists of an aluminum piston that
slides in a chrome-plated brass sleeve.The TRX 2.5 uses ABC
construction.

Air filter - The air filter sits atop the carburetor and prevents

harmful dust and dirt from entering the engine. Dirt ingestion
is the number one cause of premature engine failure so the
engine should never be run without the air filter in place.

Big Block .15 - A .15 (2.5) engine that uses a larger crankcase

size and longer stroke than typical .15 engines. Generally only
used for specific racing classes.

Break-in - Break-in is the procedure for running a brand new

engine according to specific instructions.This correctly
prepares the engine for normal running.The break-in
procedure can be different for different makes of engines.
Follow the Traxxas directions for break-in exactly.

Carb - Abbreviation for carburetor.
Carburetor - The carburetor atomizes (mixes) the fuel with the

air so that the engine can burn it. There are two types of
carburetors, slide carbs and barrel carbs. The TRX 2.5 uses the
superior slide carburetor design.

Clean-out - Cleaning-out is a condition that occurs when the

engine is accelerating and the fuel mixture becomes
sufficiently lean to allow the engine to continue into its upper
RPM power band. Usually characterized by a noticeable
decrease in blue exhaust smoke and a dramatic increase in
engine speed.

Combustion chamber - The combustion chamber is machined

into the bottom of the cylinder head.This is where the glow

plug ignites the fuel.The shape of the combustion chamber is
designed to promote more efficient burning of the fuel.

Connecting rod - The connecting rod transfers the piston

motion to the crankshaft.The TRX 2.5 racing engine uses a
“knife-edged” connecting rod. The aerodynamic, sharpened
edges allow it to “slice” through the pressurized air/fuel
mixture inside the crankcase.

Cooling fins - The cooling fins are molded into the cylinder

head and crankcase and cause heat to be drawn away from
the engine. Heat is removed when it dissipates into the air
passing across the cooling fins. It is important to keep the fins
clean of dirt and debris for maximum cooling efficiency.

Crankcase - The engine “body” that contains all of the running

mechanical components.

Crankshaft - The main shaft of the engine that contains the

rotating assembly.

Cylinder head (head) - The finned aluminum part on top of the

engine that is responsible for dissipating most of the engine’s
heat. The combustion chamber is machined into the bottom of
the head.

Dyno - Abbreviation for dynamometer. A precise piece of

testing equipment that accurately measures engine power
and torque output over the engine’s entire RPM range.

EZ-Start - Second generation Traxxas on-board electric starting

system.The system consists of a hand held starter control unit
and an on-board gearbox with an electric motor to spin the
engine.The new EZ-Start contains many performance and
reliability improvements over the first generation EZ-Start.

Filter foam - The oiled foam element inside the air filter

housing.The filter foam in the TRX 2.5 must be thoroughly
cleaned and re-oiled after every hour of run time.

Fit - Usually refers to the fit of the piston and sleeve. If the fit is

tight, then the piston will feel very tight at top of the sleeve
and the engine will have good sealing and compression. If the
fit is loose, then compression will be low and the piston and
sleeve should be replaced.

Learn terms related
to the TQ Radio
System on page 12.

23

The TRX 2.5 Racing Engine

Flame-out - Occurs when the engine stops running at high

RPM. Usually the fault of an excessively lean fuel mixture or
glow plug failure.

Fuel - (10% 20%) The TRX 2.5 must have model engine fuel to

run. Traxxas Top Fuel is recommended. Fuel is sold in quarts
and gallons from hobby dealers.The 10 and 20% labeling
refers to the percentage amount of nitromethane contained in
the fuel (see “nitro percentage” definition).

Fuel mixture - The ratio of fuel to air as determined by the

needle settings of the carburetor.

Fuel tubing (fuel line) - The thick silicone tubing that carries

fuel from the fuel tank to the carburetor.

Glow plug - The glow plug is located in the cylinder head at the

top of the combustion chamber.It contains a platinum
element that glows red hot when voltage is applied.When the
engine is being started, the heat from the glow plug ignites
the fuel mixture and starts the combustion process.

Glow plug driver - This tool clips onto the glow plug and

supplies the required voltage to light the glow plug element. It
is also called an igniter.EZ-Start equipped engines do not
require this separate tool.

Header - The aluminum tube that connects the exhaust system

to the engine exhaust port. The length and diameter of the
header must be carefully selected to extract the most power
from the engine.

High-speed needle - Adjusts the carburetors fuel/air mixture at

high RPM.

Idle speed - The speed (RPMs) the engine runs at when the

transmitter’s throttle trigger is at neutral.

Idle speed screw - Located on the carburetor body.

This screw adjusts the idle RPM of the engine.

Lean - A running condition where the engine is not getting

enough fuel (for the available air). Symptoms include engine
overheating, or the engine runs for a short time and then

stalls, particularly at high speed. This is a dangerous
condition that should be corrected immediately or it can
ruin your engine.

Leaning the mixture - Turning either the high speed and/or

low-speed needle(s) clockwise to decrease the amount of fuel
the engine receives.

Low-speed needle - Needle valve that controls the low-speed

fuel mixture.

Needle valve - Valve consisting of a tapered needle that closes

against a corresponding seat to regulate fuel flow.

Nitro - Abbreviation for nitro methane, a component of model

engine fuel that improves fuel combustion and power output.
Nitro also refers to a class of RC powered by model engines
instead of electric.

Nitro content - The amount of nitro methane used in the fuel.

Usually measured as a percentage of the total fuel volume.
Traxxas engines are optimized to use 10-20% nitro. 30% nitro
may be used for racing.

Nitromethane - Nitro methane is a component in the fuel that

increases power from the combustion process up to a point.
Engines are generally optimized to use a range of nitro
content for the best power.

O-ring - Rubber “O”-shaped ring used as a sealing gasket.
Pipe - Abbreviation for the tuned exhaust pipe on a nitro

engine. See “Tuned Pipe” definition.

Piston - The piston is the internal engine part that is attached to

the upper end of the connecting rod and moves up and down
in the cylinder sleeve.The precise fit between the piston and
the sleeve creates a seal that allows engine to have the
required compression for combustion.

Port - Ports are openings in the sleeve that allow atomized fuel

to enter the combustion chamber and burned exhaust gasses
to exit. The shape and location of the ports are a large factor in
controlling the engine timing and power output.

24

Priming - Manually causing fuel to move from the fuel tank up

to the carburetor.This is sometimes necessary after the engine
has been sitting for a long period of time and all the fuel has
drained back to the tank. On a Traxxas model this is done by
holding your finger over the exhaust tip for one or two
seconds while the engine is starting.

Punch - A term that refers to how quickly the model responds

to throttle input or how quickly it accelerates.

Rich - A running condition where the engine is getting too

much fuel for the available air. It is better to run an engine
slightly rich to increase engine life. Excessively rich mixtures
cause the engine to have sluggish performance with
exaggerated blue smoke and unburned fuel coming from the
exhaust.

RPM - Abbreviation for revolutions per minute (how many times

the engine crankshaft spins in a minute).

Sleeve - Internal engine part that contains the piston. The

precise fit between the sleeve and the piston creates a seal
that allows engine to have the required compression for
combustion.The sleeve in a TRX engine is made of brass and is
then hard-chrome plated.

Slide carburetor - The throttle on a slide carburetor closes and

opens by sliding a barrel in and out of the carburetor body.
This type of carburetor is preferred for performance use
because it provides a less restrictive “straight-through” air path
than the barrel carburetor design.

Stall - When the engine stops running, usually due to an

incorrect fuel mixture setting or running out of fuel.

Tuned pipe - The tuned exhaust pipe usually consists of a

specially-shaped metal or composite chamber with baffles
that is designed to enhance the power output of the engine.

Wear-in - Fitment process that occurs during engine break-in

where internal engine parts develop an even more precise
matched fit through actual use under controlled
circumstances.

WOT - Abbreviation for wide-open throttle.

The TRX 2.5 Racing Engine

25

The TRX 2.5 Racing Engine

The Fuel

Use the Right Fuel

It’s imperative that you use the correct fuel in
your TRX 2.5 for maximum performance and
engine life.Traxxas Top Fuel should be used
to ensure correct engine lubrication,
performance, and ease of tuning.Traxxas Top
Fuel has been proven in thousands of engines,
so you can count on it every day for great
performance.

Top Fuel is the only fuel which is 100% certified for use in
Traxxas engines.
Traxxas Top Fuel is made with just the right balance of the
highest grade natural and synthetic lubricants to allow
excellent throttle response and the best top-end
performance, without sacrificing long-term durability.
All of the components in the fuel are carefully selected from
the best materials available and then custom blended to
match the metallurgy and temperature characteristics of
Traxxas engines.

You may use 10% or 20% nitro-content fuel. Use the same
percentage all the time; don’t switch back and forth between
10% and 20% fuel. If you break-in your engine on 20% fuel, then
always use 20% fuel.

What about Other Fuels?

Can other brands of fuel be used besides Top Fuel? There are
other fuels that can provide satisfactory performance; however
there could be long-term costs in the form of decreased engine
performance, loss of tuning ease, and shorter engine life.

Everyone has an opinion or a claim to make about fuel. The
engineering team at Traxxas spent over 2-years developing the
TRX 2.5 racing engine. No one knows more about the specific
fuel requirements of Traxxas engines than Traxxas engineers. We
strongly urge you not to take chances with your engine
investment and use the Traxxas fuel made for the TRX 2.5.

Handling the Fuel

Follow all directions and warnings on the fuel can.

Keep the fuel tightly capped at all times. Some components
in the fuel can evaporate very quickly and upset the balance
of the fuel.
Do not store unused fuel in the fuel dispenser.Immediately
return fresh unused fuel back into the fuel can.
Do not mix old and new fuel. Never mix different brands of
fuel together.
Store the fuel in a cool dry location, away from any source of
heat, ignition,or combustion.
Read and follow the safety precautions on
page 5 in this manual.

Filling the Fuel Tank

Use a fuel dispensing bottle (Traxxas Top
Fueler, part# 5001) to put fuel into the Nitro
4-Tec’s fuel tank. To fill the fuel bottle,
squeeze the air out, insert the dispenser
tip into the fuel can, and release your grip
on the bottle. As the bottle
expands, fuel will be drawn
into it.

To fill your model flip up the
spring-loaded cap on the fuel
tank, insert the tip of the fuel
bottle, and squeeze to
dispense the fuel. Fill the tank
until the fuel level reaches the base of the filler neck. Close the
fuel tank lid, making sure it closes tightly.

▼▼▼▼ ▼▼

▼▼▼

You may use higher
nitro percentages

than 20% in certain
circumstances. Call 1-888­TRAXXAS for more
information.

26

The Air Filter

The TRX 2.5 air filter is carefully designed to deliver maximum
performance while protecting your engine from dust and dirt.
Use only the supplied filter.You will not improve engine
performance by switching to an aftermarket filter, and you
may risk engine damage due to poor filtration.

The TRX 2.5 air filter assembly consists of 3 pieces:

1. A rubber filter base

2. A plastic housing consisting of a permanently assembled

mesh cap and body

3. An oiled foam element

You must clean the filter after every hour of runtime, even if the
filter looks clean. Dust (which is often too fine to see) and dirt
constantly move through the filter anytime the engine is
running. Even if you can’t see dirt on the filter,it is present inside
the foam after any amount of runtime. If you exceed the
recommended cleaning intervals, your engine will be damaged.
Engine damage or wear due to dirt ingestion is easy to detect,
and one of the top causes of premature engine failure.

Air Filter Cleaning Instructions

1. Remove the air filter from the

carburetor bore by pulling
the entire filter firmly to the
side to release it. Do not pull
straight up.

2. Disassemble the filter.Pull the

rubber base out of the filter
body.With the base removed, the foam element is visible in
the bottom of the filter body.Pull out the foam element.

3. Clean the filter parts by thoroughly washing all three pieces of
the filter assembly in hot soapy water (dishwashing detergent
works well). Repeat twice.

4. Thoroughly dry the parts with a clean towel or compressed air.
Remember to wear your safety glasses when working with
compressed air.

5. Oil the foam element by saturating it with foam filter oil.Use
the supplied Traxxas filter oil (part# 5263) or a high-quality,
special-purpose foam filter oil like what is used for high­performance motorcycle and ATV engines.This type of filter oil
is available at motorcycle pro-shops.Never run the engine
without a properly oiled filter! Apply 30 drops of the Traxxas
filter oil evenly to the top,bottom and sides of the filter
element (30 total drops divided among the 3 surfaces).
Squeeze the filter element repeatedly to help spread the oil
throughout. Squeeze the excess oil from the foam.The filter
element should be evenly colored by the oil. Even color
indicates that the oil is evenly distributed. Note: Do not use

the air filter oil for anything other than the air filter. It is not
meant to be a lubricant.

6. Reassemble the filter and install it on the engine,making sure
the rubber base fits securely on the carburetor with no gaps or
air leaks.

The TRX 2.5 Racing Engine

Clean your air filter
after every hour of

runtime to avoid
engine damage, even if the
filter looks clean.

If you use

compressed air to

dry your air filter
assembly, wear safety
glasses and avoid directing
compressed air toward
your skin.

27

The TRX 2.5 Racing Engine

The Carburetor

Understanding the Carburetor adjustments

The carburetor performs several functions. It controls the
engine’s speed by restricting the intake of air and fuel into the
engine. It atomizes the fuel (suspends the fuel droplets in the
air) and also controls the air/fuel ratio of the mixture entering
the engine (how much air for a given amount of fuel).

To help provide a better understanding of engine tuning and
why it’s necessary, the following is a brief explanation of the
air/fuel combustion process that takes place inside the engine.

In order to create the cylinder pressure that results in power, the
engine burns the air/fuel mixture. Both air and fuel,in correct
amounts, are needed for proper combustion. It is the
carburetor’s job to mix the air and fuel together (atomize the
fuel), in the correct proportion for the best possible combustion.
This is the ideal air/fuel ratio.The ideal air/fuel ratio required for
the engine remains roughly constant. Due to variations in
atmospheric conditions (temperature, humidity, altitude etc.)
fuel flow adjustment valves (called fuel mixture needles) are
required to meter the fuel and maintain the ideal air/fuel ratio in
these ever-changing conditions. For example, colder air is more
dense (more air molecules) for a given volume of air and
therefore requires more fuel (more fuel molecules) to maintain

the correct air/fuel ratio.Warmer air is less dense (fewer air
molecules) and therefore needs less fuel to maintain the correct
air/fuel ratio.The tuning needles are there to adjust how much
fuel is made available for the carburetor to mix with the
available air (atomization).

The Fuel Mixture Needles

The amount of fuel metered and atomized by the carburetor is
controlled by the two mixture needles, the high-speed needle
and the low-speed needle.The low-speed needle is used to
meter the fuel used by the engine at idle and low RPM (part­throttle) engine speed.The high-speed needle is used to meter
the fuel when the throttle is open from part throttle to wide­open throttle (WOT).Two needles on the TRX 2.5 provide precise
control of the air/fuel ratio across the engine’s entire RPM range.

The maximum possible fuel flow is always controlled by the
high-speed needle. It works like the main water valve on a
garden hose.Turn it clockwise to close the valve,counter­clockwise to open it. When the throttle is at idle or partially
open, the low-speed needle again meters the fuel flow at the
outlet (needle seat) where the fuel enters the carburetor venturi.
This second valve acts like the spray nozzle at the end of the
garden hose in our example.When you accelerate from idle, the
throttle opens and the low-speed needle is pulled away from
the needle seat. This allows more fuel to flow with the increased
air flow.As the throttle is increased, the low-speed needle is

28

See page 35 for
more information
on how air density

affects engine tuning.

Air

Fuel

Dense Air Less Dense Air

pulled completely away from the needle seat leaving it fully
open. At that point, fuel metering is entirely controlled by the
high-speed needle. Again, using our water hose example,when
the spray nozzle at the end of our garden hose is fully open,
then the main water valve can be used to adjust how fast the
water flows.

The engine’s performance is directly linked to the fuel
mixture. Richening the fuel mixture increases the amount of
fuel in the air/fuel mixture ratio and leaning the fuel mixture
decreases the amount of fuel in the air/fuel mixture ratio.

Slightly lean fuel mixtures deliver stronger,more efficient
combustion and more power, but with less lubrication.

Slightly rich fuel mixtures deliver cooler running and more
lubrication but with slightly less power.

Tuning the engine means finding the perfect balance between
the two; excellent power to meet your needs while maintaining
good lubrication for long engine life. The optimal fuel mixture
setting is rich to provide a safety margin against having a lean
condition if some variable changes (such as the temperature
from one day to the next).

General fuel mixture settings are measured by the number of
turns the needles are turned out from fully closed.The fuel
mixture settings have been pre-set from the factory to typical
break-in settings. Do not readjust your carburetor from the
factory settings until after the engine is started and running,
and you have been able to observe the engine running to
assess what minor adjustments may be required to compensate
for fuel, temperature, and altitude.Adjustments are usually
made in 1/8 or 1/16-turn increments.

The Idle Speed Adjustment

The idle speed screw controls the closed position of the throttle
slide.When the throttle servo is in its neutral position, the
throttle slide should be stopped against the idle adjustment
screw.Always use the idle speed adjusting screw to control
engine idle. Do not use the throttle trim on the transmitter to
adjust idle speed. The idle speed should be set as low as
possible and still maintain reliable running.

▼▼

The TRX 2.5 Racing Engine

Water Valve

(Controls Overall Flow)

High Speed Needle

Water Nozzle

(Controls Fine Flow)

Low Speed Needle

See Tuning the TRX

2.5 for Best

Performance on

page 34 for complete
information on adjusting
the air/fuel mixture and
idle speed.

If your factory
preset carburetor

adjustments have
been tampered with, use
the following settings: set
the low-speed needle so
that the screw head is flush
with the end of the slide.
Set the high-speed needle
to 4 turns out from closed.
Always use the factory
settings for initial starting.
Only use these settings
when the factory settings
have been lost.

29

Lean

Rich

The TRX 2.5 Racing Engine

30

The Traxxas EZ-Start Electric Starting System

The Traxxas EZ-Start brings the convenience of push-button
electric engine starting to your Nitro 4-Tec.The EZ-Start consists
of a hand-held control unit and an on-board motorized starter.

Power for the EZ-Start system comes from a 7.2-volt
rechargeable NiCad battery pack installed in the hand-held
control unit (battery not included).
The engine glow plug is heated automatically by the
EZ-Start system, eliminating the need to keep up with a
separate glow plug igniter.
The voltage to the glow plug is kept constant, regardless of
the load placed on the starter by the starter motor.
The “Glow Plug”LED (light emitting diode) on the control
unit indicates the condition of the glow plug.
The “Motor” LED indicates the status of the EZ-Start electric
starter motor.
The cush drive mechanism in the drive unit prevents
damage to the gears caused by engine kickback.
Smart Start™protection circuitry prevents damage to the
motor by cutting power if the load on the motor or other
electronics exceeds safe limits.

Installing the EZ-Start Battery

The EZ-Start system requires a fully charged 7.2-volt NiCad
battery pack (not included). Use a charger (not included)
designed for 7.2-volt battery packs. Charge the battery
according to the charger manufacturer’s directions.

1. Press the tab in the end of the battery compartment door
to open

2. Plug a fully charged 7.2-volt NiCad battery pack into the
connector inside.

3. Twist the battery 2 or 3 times to twirl the battery plug wires.
This helps hold the wire and battery in place when the
battery is installed in the compartment

4. Place the battery into the compartment and press the wires
securely into place.

5. Slide the battery compartment door back on and lock the
end tab.

▼▼▼▼▼ ▼ ▼

Use the
Right Charger

The most convenient
type of charger is an AC
peak-detecting charger that
plugs directly into an AC
wall outlet. It contains
special peak-detection
circuitry that automatically
shuts the charger off when
the battery is fully charged.

If you’re using a 15-minute
timed charger, always fully
discharge the battery pack
before each charge. Some
high mAh battery packs
(1500 mAh or higher)
require more than the
standard 15 minutes of
charge time. If the battery
pack is cold after 15 minutes
of charging, add another 5
minutes of charge time.
Closely monitor the battery
pack and stop charging it
when it begins to feel warm
to the touch. Never leave a
battery charging
unattended. Always follow
charger manufacturer’s
instructions.

The TRX 2.5 Racing Engine

Using the EZ-Start

Your EZ-Start controller plugs
into a 4-prong receptacle
mounted on the rear shock
tower of your Nitro 4-Tec. When
the red button on the controller
is depressed, the EZ-Start motor
begins to spin the engine, and
power from the control unit heats the glow plug.Assuming all
settings and preparations are correct, the engine should start
almost immediately.

Each of the two status indicator
LEDs on the hand-held control unit,
the Motor LED and the Glow Plug
LED, should light green while
starting. If either LED fails to light
while starting, there is a fault
indicated with that function:

If the Glow Plug LED fails to
light, the glow plug may be bad,
or the glow plug wire may be
damaged or disconnected.

If the Motor LED fails to light
and the starter fails to operate,
then the EZ-Start is in
protection mode.

Protection Mode

The EZ-Start uses Smart Start™technology to monitor the
condition of the system and detect failures.The controller
monitors the load being placed on the EZ-Start motor. If the
load becomes excessive,the system shuts off power to the
motor to prevent costly damage to the motor and the
controller.This may occur, for example, if the engine floods with
fuel during starting. The starter spins at first but when excessive
fuel in the combustion chamber begins to lock up the engine,
the starter motor slows under the heavier load.This causes the
protection circuit to shut off the power to the motor. Allow at
least 3 minutes for the starter motor to cool and the circuit to
automatically reset before continuing.Use the time to find and
eliminate the condition that caused the excessive load on the
starter motor.

▼▼

When the EZ-Start
controller is in

protection mode, wait
at least three minutes before
attempting to start the
engine, to give the starter
motor time to cool.

It’s normal for your

EZ-Start controller

to become warm
after repeated use.

See page 43

for information

on clearing a
flooded engine.

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

31

The TRX 2.5 Racing Engine

32

See Important
Points to Remember

on page 5 for other

precautions.

Never run your
Nitro 4-Tec indoors.

Since the TRX 2.5
racing engine exhaust
fumes are harmful, always
run your Nitro 4-Tec
outdoors, in a well­ventilated area.

Your TRX 2.5 racing

engine doesn’t

usually require
priming. If you do need to
prime your engine, watch
the fuel line carefully to
avoid flooding your engine.
See page 43 for
information on clearing a
flooded engine.

Your carburetor is

pre-set at the

factory to give the
correct air-to-fuel ratio and
idle speed for engine
break-in. Do not adjust the
carburetor unless you
observe a poor running
condition that requires
correction.

Breaking-in Your TRX 2.5 Racing Engine

The TRX 2.5 uses a ringless,aluminum-brass-chrome (ABC)
piston/sleeve construction.This type of engine design relies on a
very precise running fit between the piston and sleeve for cylinder
sealing. Engine break-in is necessary to allow the piston and

sleeve to develop an extremely precise fit and optimum cylinder
sealing. Therefore, proper engine break-in is critical to achieving
the fastest, most reliable engine performance.

Allow yourself about 1 to 11/2hours to complete the break-in
procedure.The engine break-in period will take 5 tanks of fuel in a
Nitro 4-Tec.The break-in time is not the time to impress your
friends with your new Nitro 4-Tec. You must wait until the engine

is fully broken in before attempting sustained high speed
running. Patience and careful attention during break-in will reward

you with the best-performing TRX 2.5 possible.

During break-in, your engine may appear to malfunction with
symptoms like stalling, inconsistent performance, and fouled glow
plugs.These are simply the normal “break-in pains” engines
sometimes go through.They will disappear once your engine is
fully broken in. Many owners report not experiencing any of these
symptoms with the TRX 2.5.We recommend replacing the glow

plug with a new one after the engine break in procedure.

Engine Break-in Procedure

The focus during break-in is to vary and limit the engine speed.
This will be accomplished by accelerating and stopping at different
rates for the first 5 tanks of fuel. As the engine begins to break-in,
the duration and intensity of the acceleration will gradually
increase. Sustained high-speed running is not permitted until the
6th tank of fuel. Perform the initial break-in on a large,flat, paved
surface. Apply all throttle and braking actions gently. Abrupt

acceleration or braking could cause the engine to stall
unnecessarily.

Special break-in fuels are not recommended.Use the same fuel
you plan to use everyday.
If possible, avoid breaking-in the engine on extremely hot or
cold days.
Pay careful attention to the fuel level. Do not allow the fuel tank

to run completely empty. An extremely low fuel level causes
the mixture to run too lean.This could result in a burned glow
plug or extremely high engine temperatures.
Keep extra glow plugs handy (Traxxas part #3231). The break-in
process can cause deposits to form on the plug leading to plug
failure.

Follow the instructions exactly for each of the first 6 tanks of fuel.

Starting Your TRX 2.5 Racing Engine for the First Time

Before you start your TRX 2.5 racing engine for the first time, make
sure you have read all instructions and precautions in this manual.

Pay close attention to the tank-by-tank break-in instructions in
the next section, and make sure you have read and understood
them before you run your engine.

Your engine must be at room temperature (70°F or 21° C) or
above the first time you start it.If it’s cooler than room

temperature outside,keep your Nitro 4-Tec indoors until you’re
ready to start it, then take it outside.

1. Turn on the radio system according to the instructions
on pages 18 and 19.

2. Make sure the throttle is in the idle position.

3. Connect the EZ-Start controller according to the instructions on

page 31.

4. Press the starter button and watch for fuel moving through the
fuel line up to the carburetor.Watch closely! The fuel moves very
fast. If the fuel doesn’t move through the line within 5 seconds,
prime the engine by briefly (one or two seconds) covering the
exhaust outlet until the fuel is just visible in the carburetor fuel
line. Watch carefully! If the engine is primed too long, it will

flood with fuel and stop turning.

5. Once fuel reaches the carburetor, the engine should quickly start
and idle.

6.Disconnect the EZ-Start controller from the model.

7.Proceed with the engine break-in.

If your engine doesn’t start, see Troubleshooting Your Nitro 4-Tec
on page 42.

▼

▼▼▼

The TRX 2.5 Racing Engine

33

As you gain
experience in the

hobby, you may
discover that many people
have differing opinions on
what is the proper
procedure to break-in a
model engine. Only use the

Traxxas break-in procedure.
Other break-in procedures
could result in a weak,
damaged, or otherwise poor
performing engine. The

procedure outlined here
was extensively tested and
proven to yield better
performing engines than
other “common” break-in
methods. Even if you have
years of experience using
model engines, please do
not ignore this caution!

Tank 1

1. Drive the model with the body off.

2. Driving procedure: Gently pull the throttle trigger to 1/4

throttle over a 2-second count. Then gently apply the brake to
stop.Count the two seconds out while accelerating: one

thousand one, one thousand two, and then stop. Operate the
throttle trigger as smoothly as you can. Repeat this starting and

stopping procedure until the first tank of fuel is nearly empty.

3. Look for thick blue smoke exiting the exhaust outlet. If there is
no smoke, richen the high-speed needle 1/4 turn, by turning the
needle counterclockwise.

4. When the fuel tank is nearly empty,shut off the engine by
pinching the fuel line connected to the carburetor.

5. Let the engine cool for 15 minutes.

Note: If at any point the engine cuts out or stalls during gentle
acceleration, richen the high-speed needle 1/4 turn by turning the
needle counterclockwise.

Tank 2

1. From tank 2 forward,the Nitro 4-Tec should be driven with the

body on.

2. Driving procedure: Gently pull the throttle trigger to 1/2
throttle over a 2-second count. Then gently apply the brake to
stop. Count the two seconds out while accelerating: one
thousand one, one thousand two, and then stop. Repeat this
starting and stopping procedure until the second tank of fuel
is nearly empty.

3. When the fuel tank is nearly empty, shut off the engine and let it
cool for 15 minutes.

Tank 3

1. Driving procedure: Gently pull the throttle trigger to 1/2

throttle over a 3-second count. Then gently
apply the brake to stop. Count the three

seconds out while accelerating: one thousand
one, one thousand two, one thousand three,
and then stop. Repeat this starting and

stopping procedure until the third tank of
fuel is nearly empty.

2. As the engine loosens, the idle speed may increase and cause
the model to try to creep forward when stopped. Reduce the
idle speed by turning the idle adjustment (see page 22) on the
carburetor counterclockwise.

3. When the fuel tank is nearly empty, shut off the engine and
refuel. From here on, you do not need to let the engine cool
between tanks.

Tank 4

1. Driving procedure: Gently pull the throttle trigger to full

throttle over a 3-second count. Then gently apply the brake to
stop. Count the three seconds out while accelerating: one

thousand one, one thousand two, one thousand three, and then
stop. Repeat this starting and stopping procedure until the

fourth tank of fuel is nearly empty.

2. Apply the throttle gradually! Your finger should not reach full
throttle until the end of the three-second count.

3. Keep your driving smooth and consistent.

4. When the fuel tank is nearly empty, shut off the engine and

refuel.

Tank 5

1. Driving procedure: Gently pull the throttle trigger to full

throttle over a 3-second count, hold for 2 more seconds, and
then gently apply the brake to stop. Count the five seconds out
while accelerating.Repeat this starting and stopping
procedure until the fifth tank of fuel is nearly empty.

2. When the fuel tank is nearly empty, shut off the engine and
refuel.

Tank 6

During the sixth tank of fuel, the engine can be tuned for general
performance use. Proceed to the next section in this manual.

Tank

1
2
3
4
5

Throttle

1/4
1/2

1/2
Full
Full

Time

2 Seconds
2 Seconds
3 Seconds
3 Seconds
5 Seconds

Cool

15 Minutes
15 Minutes

-

-

-

Body

Off
On
On
On
On

Notes

Apply throttle gradually.
Apply throttle gradually.
Reduce idle speed if necessary.
Keep your driving consistent.
Accelerate over 3 second count,

hold for 2 seconds.

34

The TRX 2.5 Racing Engine

When adjusting the
low-speed fuel

mixture, it is very
important to make several
high-speed runs with the
Nitro 4-Tec between
adjustments to clear out any
excess fuel. Perform the
pinch test immediately after.
If the engine is allowed to
idle for a long period of time,
it could “load up” with fuel
and give you an inaccurate
measurement from your
pinch test.

For your

convenience, the

low-speed needle
has a positive stop that
prevents it from being over
tightened and damaging the
needle and seat. This also
provides an easy way to
gauge how many turns out
from closed the low-speed
needle adjustment is set to.

When tuning for

performance, watch

closely to notice
when there is no longer any
increase in speed or power
when the high-speed
mixture is lean. If you lean
the high-speed mixture to
the point that the engine
cuts-out, hesitates, or stalls,
you are well into the danger
zone and engine damage is
likely. Richen the high-speed
needle 1/4 turn and retune.

Tuning the TRX 2.5 for Best Performance

The engine’s performance depends on the fuel mixture. Turn the
mixture needles clockwise to lean the fuel mixture and
counterclockwise to richen it. Leaning the fuel mixture will
increase engine power up to the engine’s mechanical limits.

Never run the engine too lean (not enough fuel flow). Never
lean the engine until it begins to cut-out or stall. Leaning the
engine beyond the safe allowable limits will result in poor
performance and almost certain engine damage. Indications

of an overly lean mixture include:

Cutting out or sudden loss of power during acceleration.

Overheating (temperature beyond 270° F at the glow plug)
Little or no blue smoke coming from the exhaust.

If any of these conditions are present, stop immediately and
richen the high speed mixture 1/4 turn. The engine will
probably be slightly rich at that setting and you can then retune
for performance. Always tune for performance by starting rich
and moving leaner toward the ideal setting.Never try to tune
from the lean side.There should always be a light stream of blue
smoke coming from the exhaust.

Before you begin tuning,the engine should be warmed up to its
normal operating temperature and running slightly rich. All final
tuning adjustments must be made to the engine at its normal
operating temperature.You can tell the engine is running rich
by noting any of the following:

Sluggish acceleration with blue smoke coming from
the exhaust.
There is unburned fuel spraying from the exhaust tip
Leaning the high-speed fuel mixture increases performance

High-Speed Fuel Mixture Adjustment

With the engine warm and running at a rich setting, gradually
lean the high-speed fuel mixture in 1/16 turn increments. Make
several high-speed passes with the Nitro 4-Tec after each
adjustment to clear out the engine and note any change in
performance. The TRX-2.5 is extremely powerful. Remember to
apply the throttle gradually to prevent loss of control.Continue

this procedure until there is no longer any performance
improvement.If any one of the following conditions occurs, the
fuel mixture is already past the maximum safe lean setting:

1.

The engine begins to cut out at high speed

(Danger!)

2.

There is a sudden loss of power during acceleration

(Danger!)

3.

The engine begins to overheat.Symptoms of
overheating include:

Steam or smoke coming from the engine (not exhaust)
Hesitation or stalling during acceleration
Popping or clattering sound when decelerating
(detonation)
Fluctuating idle speed
Temperature measurement above

270° F

at the glow plug

Richen the high-speed needle at least 1/4 turn counterclockwise
and retune for performance.

▼▼ ▼▼▼

▼▼ ▼ ▼▼▼

The TRX 2.5 Racing Engine

35

Low-Speed Fuel Mixture Adjustment

The low-speed mixture is always set after the high-speed needle
is correctly adjusted.The low-speed mixture will be set using the
pinch test.

1. Once the engine is warm, do several high-speed runs to

confirm that the high-speed needle is set correctly.

2. Bring the vehicle in and pinch closed the fuel line going into

the carburetor.The engine should run for 2-3 seconds, speed
up, and then die.

3.

If the engine runs longer than 3 seconds, then lean the
low-speed needle 1/16 turn, make several more high­speed runs, and retest.

4. If the engine dies immediately without speeding up, then

richen the low-speed needle 1/8 turn, make several more
high-speed runs, and retest.

When the low-speed needle is set correctly,the engine’s throttle
response should be very quick.

Idle Speed Adjustment

Once the high and low-speed mixtures have been set, reduce
the idle speed to the minimum reliable idle speed. Remember,
this adjustment should be made while the engine is running at
normal operating temperature.

1. Tu rn the throttle trim on the transmitter so that the brakes

are applied.This ensures that the throttle slide is resting
against the idle adjustment screw.

2.

If necessary, remove the air filter to gain access to the idle
adjustment screw.

3.

Turn the screw counterclockwise to reduce the idle
speed, or clockwise to increase it. The idle speed should
be set as low as possible while still maintaining reliable
running characteristics.

4.

Reset the throttle trim on the transmitter

Fine-Tuning the Carburetor

After fine-tuning your TRX 2.5 racing engine at the end of the
break-in procedure, no major adjustments to the fuel mixture
are usually necessary. Make note of the temperature, humidity,
and barometric pressure at the time you finished fine tuning
your carburetor.Current weather conditions can be found
online from national websites, local TV news websites, and
Television.This information will be considered your baseline
setting.You may need to adjust your carburetor needles to
compensate for changes in temperature and barometric
pressure (air density) from day to day. Generally, you’ll need to
richen the fuel mixture when the weather is colder than your
baseline temperature and the air density is higher.Lean the fuel
mixture when weather is warmer than your baseline
temperature and the air density is lower.The chart below
provides general guidelines on how weather conditions affect
air density when they move higher or lower than your baseline
setting (see page 28 for detailed info on how air density affects
mixture settings).

If the...

Humidity

Pressure (barometer)

Temperature

Altitude

Nitro %

is..

Lower
Higher
Lower
Higher
Lower
Higher
Lower
Higher
Lower
Higher

then the air density is...

Slightly more dense
Slightly less dense
Less dense
More dense
More dense
Less dense
More dense
Less dense

adjust (correct) the fuel mixture to be...

Slightly richer
Slightly leaner
Leaner
Richer
Richer
Leaner
Richer
Leaner
Leaner
Richer

Check the Traxxas
website for additional
information on base

line settings for your area.

36

Tuning the Engine by Temperature

The following procedures require an
optional infrared temperature probe
or on-board temperature gauge
(Traxxas on-board digital
temperature gauge, part#4090).
Engine temperature can be used as
an effective tuning aid when you understand the relationship
between engine temperature and ambient temperature.

The engine operating temperature,when tuned for maximum
performance, will vary according to atmospheric conditions.The
atmospheric condition that has the most influence on engine
temperature is air temperature. Expect the engine temperature
to vary almost in direct proportion to atmospheric temperature.
Assuming you tuned the engine for the same maximum
performance each day,the engine will run about twenty
degrees hotter when it’s ninety degrees outside than it would in
seventy-degree weather.For this reason, we cannot give you a
definitive temperature range that indicates the best possible
engine tuning.

The temperature gauge can aid you in tuning by giving you a
relative indication of how your adjustments are affecting the
engine and by preventing you from exceeding maximum
engine temperature. For example, as you lean the fuel mixture,
the engine performance will increase along with the
temperature. If you continue to lean the fuel mixture and the
temperature increases but the engine performance does not
change, then you have exceeded the maximum safe lean
setting.

Even if it’s 100°F outside,you should be able to tune for
maximum performance. Try to keep your engine from exceeding
270°F when measured at the glow plug. If tuning for maximum
performance results in
engine temperature
exceeding 270°F, try to
increase airflow to the
engine by cutting out
the windshield. If the
engine temperature still
cannot be kept below
270°F, richen the high­speed needle slightly.

The TRX 2.5 Racing Engine

37

Driving the Nitro 4-Tec

Introduction

Your TRX 2.5 racing engine is
broken in, the fuel mixture
is balanced, and the idle is
set…now it’s time to have
some fun! This section
contains instructions on
driving and making
adjustments to your Nitro
4-Tec.Before you go on, here
are some important precautions to
keep in mind.

Don’t run your Nitro 4-Tec through water, mud, snow, or
wet grass. Water and mud are easily drawn through the air

filter and will severely damage the engine. Small amounts of
moisture can cause electronics to fail and loss of control over
your Nitro 4-Tec.

The TRX 2.5 is extremely powerful. Remember to apply the
throttle gradually to prevent wheelies or loss of control.

Don’t hold the Nitro 4-Tec off the ground and rev the engine
excessively with no load on the engine.This practice could
result in internal engine damage.

Avoid excessive high-speed running for extended periods of
time or over long distances.This could cause the engine to
build up enough speed to exceed maximum safe RPM limits.

Don’t drive your Nitro 4-Tec with drive train damage of any
kind.The engine could be damaged due to overloads on the
engine caused by drivetrain friction, or over-revving caused
by loose or missing parts.

Don’t tow anything with your Nitro 4-Tec.The engine is
cooled by airflow created by speed.Towing creates a high
load on the engine, and at the same time limits cooling of
the engine due to low vehicle speed.

If your Nitro 4-Tec gets stuck,stop driving immediately.Move
the vehicle and then continue driving.

▼▼

▼▼▼▼ ▼

Once you become familiar with driving your Nitro 4-Tec, you may
wish to make adjustments for better driving performance.

Adjusting the Shift Point

The Nitro 4-Tec comes equipped with a two-speed transmission.
When the shift point on this transmission is adjusted correctly,it
will maximize acceleration, improve drivability, and minimize lap
times. Use a 2.0mm allen wrench to adjust the shift point.

1. Stop engine.

2. Rotate the drum until the access hole is visible from the top.

3. Hold the spur gear set, and roll the car forward while looking

through the access hole. Note
that you will see two set
screws through the access
hole as you roll the car
forward.The first one holds
the two-speed mechanism to
the shaft. Do not loosen this
screw unless you want to
remove the two-speed
mechanism. The second is the
adjustment set screw.Refer to the drawing to identify the
screws.

4. Insert a 2.0 allen wrench through the clutch drum and into
the adjustment set screw.(See diagram)

5. Turn the adjustment screw clockwise to raise the shift point
(later shifts). Be careful not to
overtighten the adjustment
screw or you may damage the
tension spring.

6. Turn the adjustment screw
counter-clockwise to lower shift
point (earlier shifts). Be careful not
to loosen the adjustment screw
too much or you may cause the
screw and spring to fall out.

7. Use 1/8 turn increments to find the approximate, desired shift
point.

8. Check performance by running a test lap after each
adjustment.

9. Use 1/8-1/16 turn increments to fine tune the shift point.

Alignment Specs

The Nitro 4-Tec is supplied with soft-compound, race-quality
tires. Due to the high power output of the TRX 2.5 Racing
Engine and the high performance nature of the tires, suspension
alignment is critical to achieving maximum tire life. Proper
alignment promotes even and consistent tire wear as well as
predictable and balanced handling.

Camber

The camber angle of both the front and rear wheels can be
adjusted with the camber rods (upper turnbuckles). Use a
square or right-angle triangle to set
the camber accurately. Adjust the front
wheels to 0 degrees of camber (wheel
is perpendicular to the ground). In the
rear,adjust the wheels to 1 to 2
degrees of negative camber. These
adjustments should be set with the car
positioned at its normal ride height.
The following information gives
recommended stock alignment
settings for the Nitro 4-Tec with stock
tires and inserts.

• Front Camber Degrees ......-1.0

• Rear Camber Degrees ........-1.0

• Front Caster Degrees* ........12.0

• Front Toe-In Degrees ............0.0

* This setting is achieved by having the 1mm
caster spacer in the front and the 2mm caster
spacer in the rear (where the upper suspension
arm attaches to the upper suspension arm
mount).

38

Adjusting Your Nitro 4-Tec

It is important that
your engine is

properly tuned and
has reached full operating
temperature before making
shift point adjustments. Stop
the engine before making
adjustments.

The transmission

may not shift if the

adjustment screw is
turned too far in (locked in
first gear), or too far out
(locked in second gear). If
the car has quick
acceleration and does not
appear to shift, the
transmission is never
reaching the shift point. The
shift point needs to be
lowered by turning the
adjustment screw counter­clockwise. If the car has poor
acceleration but very high
top speed, the transmission
is shifting into second gear
almost instantly. The shift
point needs to be raised by
turning the adjustment
screw clockwise.

Access

Hole

Drum

-1°

-2°

TO

0°

Front
Camber

Rear
Camber

39

Toe I n

Set the steering trim on your transmitter to neutral. Now, adjust
your tie rods so that both wheels are pointing straight ahead
and are parallel to each other (0 degrees toe in).This will ensure
the same amount of steering in both directions. If you run out of
adjustment, then the steering servo will have to be re-centered
(see centering your servos on page 41).

Fine Tuning the Shocks

The four shocks on your Nitro 4-Tec have
the most influence on its handling.
Whenever you rebuild your shocks,or
make any changes to the pistons, springs
or oil, always do it carefully and in pairs
(front or rear). Piston head selection
depends on the range of oil viscosities
that you have available.For example,
using a one-hole piston with a
lightweight oil will give you the same
dampening as a two-hole piston with
heavier oil.We recommend using the
one-hole pistons with a range of oil
viscosities from 10W to 50W (available
from your hobby shop).The thinner
viscosity oils (30W or less) flow more smoothly and are more
consistent, while thicker oils provide more dampening. Use only
100% pure silicone shock oil to prolong seal life.

The ride height for Nitro 4-Tec can be adjusted by adding or
removing the clip-on spring pre-load spacers. Instead of adding
spacers to increase stiffness, use stiffer springs. Adjust the ride
height so that the suspension arms are slightly above being
parallel to the ground. Note that changes in ride height will
occur when the changes in damper angle or spring rates are
made.You can compensate for ride height changes by changing
the pre-load spacers on the dampers. Generally speaking, ride
height should be set as low as possible without causing

significant bottoming of the chassis. Also, in order not to disturb
cornering balance, front and rear tire height diameters should
be equal. Replace excessively worn tires.

Belt Tension Adjustments

The Nitro 4-Tec’s front and middle
drive belts are designed to have a
high initial tension. During the break­in period, the drive belts and pulleys
will “wear in”and the belt tension will
gradually decrease.The front and
middle belt tensions can be tightened
by inserting shims under the front
bearing block. Do not tighten the
front belt tension unless there is more
than 0.25 inch (6mm) deflection at the
center of the belt (see drawing).To
tighten the belt, add the 0.1mm shim first and retest. If the belt
is still loose, remove the 0.1mm shim and add the 0.2mm shim
and retest.The rear belt tension is adjustable via belt tension

cams in the right and
left rear side plates.The
rear belt in the Nitro
4-Tec transmits most of
the engine’s power.
Because of the high
loading of the rear belt,
the tension should be
checked every 3-4

hours (20-25 tanks of
fuel) of running. If the rear belt can be deflected more than 0.25¨
(6mm) (see illustration), the belt tension cams should be rotated
rearward to the next eccentric slot.

At no time should
the body of the car

strike the ground or
interfere with the suspension
or tires. Either situation will
cause extremely
unpredictable handling.

Left side plate

(Bulkhead)

Right side plate

(Bulkhead)

Rear of car Rear of car

.25¨ (6mm)

Using Belt

Adjustment Shims

Adjusting Your Nitro 4-Tec

Gear Ratios

Another Nitro 4-Tec feature is the ability to change the
gear ratios. Currently, there are three optional gear ratios
for the Nitro 4-Tec.The stock gear ratio will provide very
high (60+ MPH) top speeds. Because of the extreme top
speed, the stock gear ratio is primarily intended for flat-out
running on large, unobstructed, paved areas. Organized, 1/10
scale, nitro touring car racing is typically done on smaller, closed
courses. For this type of racing change to a lower (higher
numerical) gear ratio.The following chart gives the four possible
gear ratios sets.The ratios are arranged from highest (lowest
numerical) to lowest (highest numerical). A brief application
recommendation follows each gear ratio set.

Nitro 4-Tec gear ratios must be changed as 1st and 2nd gear sets in
order to maintain compatible gear center distances. The gear ratio
chart gives the only four compatible ratio choices.

Changing the Clutch Bell Gears

1. Remove the right, rear wheel.Remove the E-clip from the

two-speed shaft. Slide the pulley and belt off of the shaft,
being careful not to lose the pin that sits under the pulley.

Remove the pin. Slide the spur gears off of the shaft (If you

are using optional gears, you may have to loosen the right

chassis stiffener to remove the spur gears).

2. Lock the flywheel with a flathead
screwdriver to immobilize it. Use a 2.5mm
allen wrench to unscrew the caphead

screw that holds the clutch bell
to the pilot shaft. Remove the
clutch bell.

3. To separate the gears from the
clutch bell, gently grip the clutch bell with channel-lock,
adjustable pliers. Cover the gears with a cloth to protect the
teeth. Using the pliers, unscrew the gears counter-clockwise.

4. New clutch gears simply screw onto
the clutch bell. Reinstall the clutch
bell and caphead screw onto the
pilot shaft. Reinstall the spur gears,
pin, pulley and belt.Secure them on
the two-speed shaft with the E-clip.

5. To adjust the gear mesh, first loosen the four 3x10
countersunk hex screws in the slotted holes in the bottom of
the chassis. Next, remove the two countersunk Phillips head
screws in the bottom of the chassis which hold the slotted
engine mount. The engine should now slide back and forth.
Slide a strip of thin note paper between the spur gears and
the clutch bell gears. Push the clutch bell gears against the
spur gears and tighten the screws on the bottom of the
chassis. Remove the paper and the gear mesh is now correctly
adjusted.

40

Gear

Clutch Spur Primary Overall (MPH) at
Teeth Teeth Reduc tion Reduction 36,000 RPM

Nitro 4-Tec Stock 1st 16 41 2.56 5.81 46.54
Equipment 2nd 20 37 1.85 4.19 64.47

Ratio Characteristics: Moderate acceleration, highest top speed
Recommended Application: Sp ort/recr eational running in very large areas

Optional Clutch Gears 1st 15 41 2.73 6.20 43.6
w/Stock Spur Gears 2nd 19 37 1.95 4.41 61.2

Ratio Characteristics: Good acceleration, very high top speed
Recommended Application: Sp ort/recr eation running in very large areas

Stock Clutch Gears 1st 16 45 2.81 6.38 42.4
w/Optional Spur Gears 2nd 20 41 2.05 4.65 58.2

Ratio Characteristics: Very good acceleration, high top speed
Recommended Application: Sp ort/recr eation, racing on large 1/8 scale size tracks

Optional Clutch Gears 1st 15 45 3.00 6.80 39.8
w/Optional Spur Gears 2nd 19 41 2.16 4.89 55.3

Ratio Characteristics: Explosive acceleration, moderate top speed
Recommended Application: Racing on small tracks. Recreational running in small areas.

Adjusting Your Nitro 4-Tec

Theoretical

Speed

Centering the Servos

Whenever your radio system has been removed for service or
cleaning, the servos must be re-centered prior to installing the
radio system in the model. If the radio system is installed in the
car,disconnect the servo horns from the servos.

Connect the steering servo to channel 1 on your receiver and
the throttle servo to channel 2. The white wire on each servo
cable is positioned towards the crystal. Connect the red and
black cable from the battery holder to the “batt” terminal on the
receiver.The red wire is positive and the black wire is negative.

Place fresh “AA”batteries in the transmitter and turn the
power switch on. Slide the throttle and steering trim
adjustments to to the center position. Now install fresh “AA”
batteries into the battery holder and turn the power switch to
the on position. The servos will automatically jump to their
center positions.

Turn off the battery holder switch followed by the transmitter.
The servos are now ready to be installed. Be careful not to move
the servo shaft when reinstalling the servo horns.

41

Adjusting Your Nitro 4-Tec

42

The following section addresses some very basic engine and
radio questions you may have about your Nitro 4-Tec. Most
questions arise from simple user errors or minor adjustments that
are easy to correct. If you can’t find a solution for your Nitro 4-Tec
here, then visit our Web site at www.Traxxas.com and click on the
Customer Support menu.There you will find a much more
extensive and detailed online troubleshooting area. In addition,
you may call Traxxas Customer Service at 1-888-TRAXXAS (outside
the US call 972-265-8000).

Radio system does not work properly:

If the power light on the transmitter does not come on, check
for proper battery installation and that the batteries are new
and/or fully charged. If the power light is blinking, then the
transmitter batteries are weak and should be replaced.See
page 13 for more details.
If the transmitter light is on but the radio is still not
responding,check for proper installation of the receiver
batteries and that the batteries are new and/or fully charged.
Check to make sure the on/off switch on the model is in the
on position. Finally,if there is still no response check the red
and black wires that connect the battery pack to the “batt”
terminal on the receiver (you will have to remove the receiver
cover). Make sure the wires are not pinched or damaged and
that the plug is secure in the receiver. See page 14 for more
details.

Short radio range:

If the radio range appears short, then first check to make sure
the transmitter antenna is fully extended and that the
antenna in the Nitro 4-Tec is in place and has not been cut or
damaged. Next, make sure the batteries are all fully charged.
Finally, if you are still experiencing short range, try a different
location. Sometimes there can be interference from various
sources that can cause your radio to malfunction.

Engine will not spin (EZ-Start will not turn the engine):

If neither LED on the controller lights, the EZ-Start battery
could be discharged or improperly connected.Inspect and
recharge if necessary.

If the glow plug LED lights and the motor LED does not, then
the EZ-Start controller is in protection mode. Allow the
controller to cool for at least three minutes.The circuitry
should automatically reset.
Check to make sure the wires are connected to the EZ-Start
motor in the Nitro 4-Tec.The red wire should connect to the
positive motor terminal, indicated by a red dot next to the
terminal.
The engine could be flooded. If too much fuel accumulates in
the combustion chamber at start up, the engine will
hydraulically lock. Follow the procedure on page 40 for
clearing a flooded engine.
Check for binding at the engine flywheel. If you are not able to
turn the engine by hand, the engine could be flooded, there
could be binding in the clutch system, or there could be
internal engine damage. See page 43 for info on clearing a
flooded engine and releasing a stuck piston. (Note: It is normal
for the engine to be extremely tight and hard to turn when
the piston reaches the top of the compression stroke.)

Engine extremely sluggish, hard to start, and will not idle
during tank 1 of the break in:

It is possible that the factory adjusted break-in settings on
your carburetor are too rich for your geographic location,
atmospheric conditions, or fuel brand. Extremes in
temperature,humidity,barometric pressure, and altitude can’t
always be accounted for with a single high-speed needle
setting.The symptoms described above can occur when the
air density is very low such as in high mountainous elevations,
and extremely cold temperatures. Under these conditions,
lean the fuel mixture slightly,1/8 turn, to see if there is any
improvement in starting and idling. Only lean the fuel mixture
just until the engine will run and idle reliably and then
proceed with the break in.

The contents of different brands of fuel (other than Traxxas
Top Fuel) in combination with extreme atmospheric
conditions can also make the factory preset break-in settings
too rich and cause the symptoms described above.Again, try
leaning the fuel mixture slightly,1/8 turn, to see if there is any
improvement in starting and idling.

▼▼▼▼▼▼

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Troubleshooting Your Nitro 4-Tec

43

Engine spins but will not start:

If the engine is spinning but will not start, first check to make
sure that both the motor and glow plug LEDs on the EZ-Start
controller light when the button is depressed. If the glow plug
LED does not light, make sure the blue glow plug wire is
tightly connected and is not damaged in any way.If the wire is
good, then replace the glow plug. It is normal for glow plugs to
require periodic replacement.Only use Traxxas heavy-duty
long glow plugs (part #3231).
Check to make sure the fuel is getting to the carburetor.
Remove the fuel line where it connects to the carburetor to
see if there is fuel in it. If not, you may need to prime the
engine. Reconnect the fuel line and then refer to page 32 for
instructions on priming the engine.
Check your fuel mixture settings. It may be necessary to adjust
the fuel mixture if the outside temperature or barometric
pressure has changed significantly since
the last time the engine was run (see Fine Tuning the Carburetor
on page 36).Turn the high-speed needle out
(rich/counterclockwise) 1/4 turn, hold the throttle trigger at
about 1/2 throttle and try again to start the engine. Once
started, retune the engine for performance (see page 35).
The engine could be worn.If the fit between the piston and
sleeve is loose, compression is reduced and the engine will be
difficult to start when it is warm, and may tend to stall when
running and when the throttle is closed suddenly to idle.
Engine life depends on many factors including fuel type, air
filter maintenance, needle settings, and how the engine was
used. For example, if the engine was allowed to ingest dirt
from lack of air filter maintenance or running through water,
then the internal engine components could wear out
extremely fast.

Engine performance sluggish:

Engine performance depends mostly on the fuel mixture
settings and how they compensate for the current
atmospheric conditions. Before you suspect other failures with
the engine, richen the high-speed needle at least 1/4 turn and
then retune the engine for performance (see page 35).
Try a new Traxxas 3231 glow plug.Sometimes a glow plug will
work well enough to start the engine but not be able to
deliver the engine’s full performance potential.

If the fuel mixture seems to be set correctly,make sure the fuel
is fresh. If the fuel is old, or was left uncapped for a long period,
then some of the important fuel components could have
evaporated.Try new, fresh,Traxxas Top Fuel
Check to make sure there is no binding in the driveline that
would cause excessive loads on the engine.

Clearing a Flooded Engine:

If the engine is primed for too long during startup, then it can
become flooded with fuel.When the engine is flooded it will no
longer turn due to excess fuel in the combustion chamber
preventing upward movement of the piston.Use the following
procedure to clear a flooded engine.

1. Remove the blue glow plug wire.

2. Remove the glow plug and gasket with the glow plug wrench

supplied with your model. A 5/16 nut driver will also work.

3. Tu rn the model upside down and plug in the EZ-Start controller.

4. Push the EZ-Start button for several seconds to clear the engine

of excess fuel

5. Turn the model over and reinstall the glow plug and gasket.

6. Reconnect the blue glow plug wire to the glow plug.

7. Reconnect the EZ-Start controller

8. Do not prime the engine.Pull the throttle to 1/2 throttle and

push the EZ-Start button. The engine should start immediately.

Piston Stuck at Top Dead Center (TDC):

A new engine will typically have a tight fit between the piston and
the top of the sleeve.This is a tapered fit. The fit should not be too
tight to start the engine, however a weak starter battery or one
that has not been charged fully may not deliver enough power to
crank the engine over at the appropriate RPM to keep the piston
from sticking. Make sure that you are using a good quality battery
pack that is fully charged.This is especially important with a new
engine that needs to be broken-in. If the engine is stuck at TDC,
then use a pair of needle nose pliers to grasp the flywheel from
the bottom of the engine. Rotate the flywheel counter-clockwise
when viewed from the front of the engine.You should see the
flywheel turn and you should feel the piston become unstuck
from the sleeve. Before trying to restart the engine replace the
starter battery with a freshly charged pack or a freshly charged
battery pack of better quality.

▼▼

▼▼ ▼ ▼▼▼

Troubleshooting Your Nitro 4-Tec

44

Your Nitro 4-Tec requires timely maintenance in order to stay in
top running condition. Neglecting the maintenance could allow

dirt, deposits, and moisture to build up inside the engine
leading to internal engine failure. The following procedures

should be taken very seriously.

After each hour of running:

Clean and re-oil the air filter.The instructions for this
procedure are on page 27. We cannot stress enough the

value of cleaning your air filter at the scheduled intervals.

Do not neglect your air filter maintenance!

Clean the outside of the engine of accumulated dirt, oil,and
grime. Accumulated grime will decrease the engine’s ability to
cool itself.

After each running session:

Perform after-run maintenance on the engine.This clears the
engine of destructive moisture and other corrosive deposits.

This is extremely important for the life of the engine. See
page 42 for after-run maintenance procedures.

I

nspect the vehicle for obvious damage or wear.Look for:

1. Loose or missing screws

2. Cracked, bent,or damaged parts

3. Cut or loose wiring

4. Cut or kinked fuel lines

5. Signs of fuel leakage

Inspect the gears for wear,broken teeth, or debris lodged
between the teeth.

Other periodic maintenance:

Piston/sleeve:

The life of the piston and
sleeve will vary greatly with how the
engine was used and maintained.The
piston and sleeve should be replaced
when they no longer seal effectively
(loss of compression). Symptoms include
the engine being difficult to start when
warm, stalling when warm,and stalling
when throttle is suddenly closed to idle.
Replace the wrist pin and G-clip
whenever the piston and sleeve are
replaced.

Connecting rod:

The connecting rod
should be replaced when the piston and
sleeve are replaced or after three gallons
of fuel, whichever comes first. Also
replace the piston wrist pin and G-clip whenever the
connecting rod is replaced.As with other internal engine
components, connecting rod life depends engine’s usage
and the quality and frequency of the engine maintenance.

EZ-Start:

The cush drive elements in the EZ-Start drive
unit should be inspected after 3-gallons of fuel. If the cush
drive elements appear deformed or hardened they should
be replaced. Inspect the EZ-Start gears for any signs of
wear.Damaged gears should be replaced. Coat the gears
with a thin layer of white lithium grease.

▼▼ ▼

▼▼▼▼▼

Maintaining and Storing Your Nitro 4-Tec

If the engine is
worn or damaged

enough to require
replacing the piston,
sleeve, or connecting rod,
consider exchanging your
old engine for a brand new
engine under the terms of
the Traxxas Lifetime Engine
Replacement Plan (ERP). It
could save you time and
effort. Details are in your
model’s documentation
package or on our website.

The TRX 2.5 is

designed to be easy

to rebuild. Critical
engine components such
as the crankcase,
crankshaft, and engine
bearings are made to
extremely high quality
standards and should
under normal
circumstances outlast
multiple sets of pistons,
sleeves, connecting rods,
and wrist pins
(reciprocating assemblies).
It could be more
economical for you to
continue to use your good
bearings and crankshafts,
and simply replace the
reciprocating assembly as
needed. Engine assembly is
not difficult and replacing
the reciprocating assembly
does not require any
special tools or skills.

45

Maintaining and Storing Your Nitro 4-Tec

After-run Procedure

You must perform after-run maintenance on your Traxxas
engine whenever the model will be stored for longer than a few
hours.Taking the time to prepare your engine for storage will
reward you with longer engine life, easier starting, and better
performance.

When a nitro engine is shut off, some excess unburned fuel
remains in the engine.The methanol in model engine fuel is
hygroscopic, which means it easily attracts and absorbs
moisture.This moisture can cause rust and corrosion on the
steel engine parts (crankshaft, bearings,wrist pin and starter
shaft) if the fuel is not removed from the engine.There are after
run oil products available from your hobby dealer or you can
use WD-40™,a common household lubricant. To ensure your TRX

2.5 racing engine is protected from internal corrosion, use the
following procedure:

1. Whenever possible, shut off the engine by pinching the fuel
line closed.This allows most of the excess fuel to be
consumed by the engine. Be sure the throttle is in the idle
position.You may have to pinch the fuel line closed for
several seconds before the engine stops.

2. Completely empty the fuel tank. Use your fuel-dispensing
bottle to suck out the old fuel. Do not mix the old fuel with
your fresh fuel supply.If you leave fuel in the tank,
transporting or handling your Nitro 4-Tec may cause fuel to
run into the engine.

3. With the fuel tank empty and the throttle at the idle
position, try to start the engine.The engine will most likely
start and run for a few seconds as it uses up any fuel
remaining in the engine and fuel lines.

4. Once the engine stops, clean the outside of the engine with
compressed air or spray motor cleaner.Once the engine is
clean and dry, remove the glow plug power wire, glow plug,
and air filter.

5. Open the throttle fully and spray a one-second burst of
WD-40 into the carburetor and into the glow plug hole
(Caution! Wear safety glasses to prevent spray from getting
into your eyes).

6. Place a rag or paper towel over the engine to catch any
WD-40 that may come out the carburetor or glow plug hole.

7. Connect the EZ-Start controller to the model and spin the
engine for 10 seconds.

8. Remove the rag or paper towel and repeat steps 5–7 two
more times.

9. Clean and re-oil the air filter so it will be ready for use next
time. See page 27 for air filter maintenance instructions.

10. Replace the glow plug, reconnect the glow plug power wire,
and reinstall the air filter.

Denatured alcohol
(available from

home centers and
paint supply stores) in a
spray bottle is an extremely
effective cleaner. Be sure to
wear safety glasses and
gloves when working with
denatured alcohol.

Fun fact: WD-40

™

stands for “water
displacement

attempt #40.” The WD-40

™

product used today was the
successful 40th attempt at
creating a water-displacing
lubricant. WD-40™was the
lab test label.

Be sure to follow
proper maintenance

and storage
procedures to avoid
damage to your engine and
other components of your
Nitro 4-Tec.

Don’t put the fuel

from your tank back

into your fuel jug.
Dispose of it properly,
following city or county
regulations.

Always wear eye

protection when

using compressed
air or spray cleaners and
lubricants.

46

Index

ABC 23
After-run maintenance 21, 44, 45
After-run procedure 45
Air density 28, 35
Air Filter 7, 22, 23, 27, 35, 44, 45

Cleaning 21, 27
foam 23
maintenance 43
oil 6

Air Intake 22
Air temperature 36, 43
Air/fuel mixture 28
Air/fuel ratio 28, 29, 32
Airflow 36
Alignment 38
Ambient temperature 36
Antenna (receiver) 11, 15, 42

tip 15
tube 15
wire 15

Antenna (transmitter) 11, 15, 42
Antenna Mount 7
Atmospheric conditions 28, 36, 43
Axle pins 9
Barometric pressure 35, 43
Baseline setting 35
Batteries 6, 12, 13, 14, 42-43

charging 30
installing 14
receiver 13, 14
rechargeable 13, 14
transmitter 13

Batteries, Ni-MH (nickel-metal hydride) 13
Batteries, NiCad (nickel-cadmium) 6, 12, 13, 30
Battery box 7
Battery compartment (Transmitter) 11, 13
Battery holder 11
Bearing Block 7
Bearings 45
Big Block .15 23
Binding 43
Body mount 7, 10
Brake 19
Bumper (Foam) 10
Camber 38
Carb, see also Carburetor 23
Carburetor 22, 23, 28, 43

adjustments 28
barrel 23
fine-tuning 35
slide 25
venturi 28

Channel 11, 12, 17, 18
Channel number 12
Charger 6, 30

peak-detecting 30
timed 30

Chassis 7
Clean-out 23
Cleaning 44
Clearing your frequency 12
Clutch bell 22, 40

gears 40

Combustion 28
Combustion chamber 23
Compression 24, 43, 44
Connecting rod 23, 44
Cooling fins 23
Crankcase 22, 23
Crankshaft 22, 23, 45
Crystal 12, 18
Customer service 4, 42-43
Cylinder sealing 32
Decals 9
Drive Belt 7, 39

tension 39

Drivetrain friction 37
Dyno 23
E-mail 4
Engine, TRX 2.5 7, 22, 26

"cutting out" 34
break-in 21, 23,32

driving procedure 33
cooling 36, 44
damage 27
detonation 34
failure 27, 44
flooding 31, 42-43
hesitation 34
life 43, 44
maintenance 44
overheating 34
performance 29
priming 25, 32,43

revving 37
shut off 45
sluggish acceleration 34
stalling 25, 32,34, 43, 44
temperature 34, 36
terms 23
tuning 28, 34

by temperature 36

Exhaust 5, 22
Exhaust fumes 32
EZ-Start 6, 23, 24, 30, 42

“glow plug”LED 30, 31, 42,43
“motor” LED 30,31, 42,43
battery 30, 42
controller 22, 31,42, 43, 45
cush drive 30
drive unit 22
motor 7, 22,31, 42
plug 7, 22
Protection Mode 31, 42-43
Smart Start™ 30, 31

Fit 23
Flag color 12
Flame-out 24
Flooding, see Engine; flooding
Flywheel 22, 42-43
Frequency band 12, 15
Fuel 5, 6, 24, 26, 43, 45

break-in fuel 32
fuel dispensing bottle 6, 26

Traxxas Top Fueler 26
Traxxas Top Fuel 24, 26, 43
unburned 45

Fuel flow 28
Fuel intake 22
Fuel line (fuel tubing) 7, 22, 24, 43
Fuel mixture adjustment 35

high-speed fuel mixture 34
low-speed mixture 35

Fuel mixture, see also air/fuel mixture 24, 34,
35, 43
Fuel tank 7, 22, 26, 45

emptying 45
filling 26
fuel level 32
tank lid 7

Gear Ratios 40

47

Glow plug 24, 30, 31, 32, 34, 43

driver 24
fouled 32
igniter 30
power wire 22, 43,45

Ground wire 22
Head (cylinder head) 22, 23
Head Protector 22
Header 7, 24
Hex hubs 9
Humidity 35
Idle adjustment screw 35
Idle speed 17, 24, 29, 32, 33, 34, 35
Idle Speed Adjustment 29, 33, 35
Idle Speed Screw 22, 24, 29
Jumping 37
Lean 24, 29

leaning the mixture 24
maximum safe lean setting 34-35, 36

Lubrication 29
Maintenance 44
Maintenance schedule 21
Methanol 45
Mixture needles 34

high-speed needle 22, 24,28, 35, 43
low-speed needle 22, 24,28, 35

Moisture 44, 45
Needle seat 28
Needle settings 43
Needle valve 24
Negative wire 22
Neutral (center) point 16-17
Neutral position 12
Nitro 24

content 24, 26
percentage 26

compensating for 35

Nitromethane, see also Nitro 24
O-ring 24
Oil 6

after-run 6, 45
filter 6
WD-40™ 6, 45

On/Off switch 7, 11, 18, 42-43
Over revving 37
Peak detection, see Charger
Pinch test 35

Pipe (tuned) 7, 22, 24, 25
Pipe hanger 7
Piston 24, 32

wrist pin 44, 45
stuck 43

Piston and Sleeve 43, 44
Port 24
Positive Wire 22
Power Switch 11
Pressure Line 7, 22
Priming, see Engine; priming
ProGraphix 9
Pulley 7
Punch 25
Quick Start 8, 9, 10, 13, 14, 15,
18, 19, 20, 26, 30, 31, 32, 34, 37
Radio interference 5, 20
Radio System 11, 12, 19, 42-43

adjustments 16
controls 16
range-testing 20
rules 18
terminology 12
terms 12

Range 14, 15, 18, 20, 42-43

short 42-43

Receiver 11, 12, 42

cover (box) 7, 42-43

Required equipment 6
Rich 25, 29
RPM 25

limits 37

Safety 5
Servo reversing switches 11, 16
Servos 7, 11, 12, 41

centering 41
reversing 11, 17
steering 7, 11,17, 19
throttle/brake 7, 11,16-17, 19

Shift point 38
Shipping 4
Shock Tower 7
Shocks 7, 39

fine tuning 39

Sleeve 25, 32
Smoke 34
Stalling, see Engine; stalling

Starter shaft 45
Starting, see Engine; starting
Steering mechanism 19
Steering Trim, Electronic 11, 12, 17, 19
Steering Wheel 11, 19
Storage 45
Supplies 6
Support 4, 42-43
Suspension Arms 7
Tank 1 33
Tank 2 33
Tank 3 33
Tank 4 33
Tank 5 33
Tank 6 33
Temperature, see Engine; temperature
Temperature gauge 36

digital temperature gauge 36
infrared temperature probe 36

Throttle Arm 22
Throttle Neutral Adjustment 11, 16
Throttle response 35
Throttle slide 35
Throttle Trigger 11, 16, 19
Throttle Trim, Electronic 11, 12, 16, 19, 35
Toe In 39
Tools 6
TQ, see Radio System
Transmission 7
Transmitter 12, 18, 42

indicator light 19
power indicator 11, 13

Traxxas Lifetime Engine Replacement Plan 44
Trim, see also Throttle Trim and Steering Trim
12
Troubleshooting 42-43
Turnbuckle 7
Water 43
Wear-in 25
Weather conditions 35
Wheels 9
Wiring diagram 11
WOT 25, 28
X-tal see also Crystal 12

Index