Generac Power Systems GTV-990, GTV-760 User Manual
SERVICE
MANUAL
Manual Part No. 0E2081
Printed in U.S.A
P.O. Box 297 • Whitewater, WI • 53190
Phone: (262) 473-5514 Fax: (262) 472-6505
GTV – 990/760
V-TWIN
OHVI ENGINE
Draft Approved- 04/24/03
FOREWORD
This manual has been written and published by GENERAC® POWER
SYSTEMS, INC. to aid our dealers’ mechanics, company service personnel and general consumers when servicing the products described
herein.
It is assumed that these personnel are familiar with the servicing procedures for these products, or like or similar products, manufactured
and marketed by GENERAC® POWER SYSTEMS, INC. It is also assumed
that they have been trained in the recommended servicing procedures
for these products, which includes the use of mechanics hand tools
and any special tools that might be required.
Proper service and repair is important to the safe, economical and
reliable operation of the products described herein. The troubleshooting, testing, service and repair procedures recommended by
GENERAC® POWER SYSTEMS, INC. and described in this manual are
effective methods of performing such operations. Some of these operations or procedures may require the use of specialized equipment.
Such equipment should be used when and as recommended.
We could not possibly know of and advise the service trade of all
conceivable procedures or methods by which a service might be performed, nor of any possible hazards and/or results of each procedure
or method. We have not undertaken any such wide evaluation. Therefore, anyone who uses a procedure or method not recommended by
the manufacturer must first satisfy himself that neither his safety, nor
the product’s safety, will be endangered by the service or operating
procedure selected.
All information, illustrations and specifications contained in this
manual are based on the latest product information available at the
time of publication. However, GENERAC® POWER SYSTEMS, INC.
reserves the right to change, alter or otherwise improve the product
at any time without prior notice.
Some components or assemblies of the product described in this
manual may not be considered repairable. Disassembly, repair and
reassembly of such components may not be included in this manual.
The engines described herein may be used to power a wide variety
of products. Service and repair instructions relating to any such products are not covered in this manual. For information pertaining to use
of these engines with other products, refer to any owner’s or service
manuals pertaining to said products.
RULES FOR SAFE OPERATION
DIMENSIONS AND FEATURES
4-CYCLE ENGINE THEORY
SECTION 1: GENERAL INFORMATION
SECTION 2: IGNITION
SECTION 3: CARBURETION
SECTION 4: GOVERNOR CONTROLS AND GOVERNOR
SECTION 5: CYLINDER HEAD AND VALVES
SECTION 6: ELECTRIC STARTER
SECTION 7: ALTERNATORS
SECTION 8: LUBRICATION SYSTEM
SECTION 9: ENGINE DISASSEMBLY
SECTION 10: CYLINDER AND CRANKCASE COVER
SECTION 11: CRANKSHAFT AND CAMSHAFT
SECTION 12: PISTON, RINGS AND CONNECTING ROD INSPECTION AND ASSEMBLY
SECTION 13: ENGINE ASSEMBLY
SECTION 14: SPECIFICATIONS
1
TABLE OF CONTENTS
A WORD ABOUT SPECIAL TOOLS
Many of the procedures depicted in this manual require the use of special tools. Some of
the tools required are available as Generac parts and are listed as such in this manual.
ATTENTION!
Generac Power Systems does not approve or authorize the use of these engines on All Terrain
Vehicles (ATV’s), go-carts, motorbikes, aircraft products, personal watercraft, or vehicles
intended for use in competitive events. Use of these engines in such applications could result
in property damage, serious injury (including paralysis), or even death.
If you do not understand any portion of this manual, contact Generac or your nearest Generac Authorized Service
Dealer for starting, operating and servicing procedures.
Throughout this publication and on tags and decals affixed
to the engine, DANGER, WARNING and CAUTION blocks
are used to alert you to special instruction about a particular operation that may be hazardous if performed incorrectly
or carelessly. Observe them carefully.
These safety warnings cannot eliminate the hazards that
they indicate. Strict compliance with the special instructions
while performing the service plus “common sense” are major
measures to prevent accidents.
The following definitions apply to DANGER, WARNING,
CAUTION and NOTE blocks found throughout the manual.
These safety symbols indicate the following:
DANGER: After this heading you can read handling, installing, operating or servicing instructions
that, if not strictly complied with, will result in
personal injury.
WARNING: After this heading you can read handling, installing, operating or servicing instructions
that, if not strictly complied with, may result in personal injury.
CAUTION: After this heading you can read instructions for handling, installing, operating or servicing
the engine that, if not strictly complied with, may
result in damage to equipment and/or property.
NOTE: After this heading you can read explanatory
statements that require special emphasis.
These symbols indicate the following:
Points out important safety information that, if not
followed, could endanger personal safety and/or
property of yourself and others.
Potential explosion hazard.
Potential fire hazard.
Ꮨ
Potential electrical shock hazard.
RULES FOR SAFE OPERATION
Study these RULES FOR SAFE OPERATION carefully before
operating or servicing this equipment. Become familiar with
the OWNER’S MANUAL and with the engine. The engine can
operate safely, efficiently and reliably only if it is properly operated and maintained. Many accidents are caused by failing
to follow simple and fundamental rules or precautions.
Generac cannot possibly anticipate every possible circumstance that might involve a hazard. The warnings in this
manual and on tags and decals affixed to the equipment, are
therefore, not all-inclusive. If you use a procedure, work
method or operating technique Generac does not specifically
recommend, you must satisfy yourself that it is safe for you
and others. You must also make sure the procedure, work
method or operating technique that you choose does not
render the engine to be unsafe.
DANGER: Do not tamper with the engine governed speed. High operating speeds are dangerous
and increase the risk of personal injury or damage
to the equipment. Operating at low speeds with
heavy load may shorten the engine’s life.
BEFORE OPERATING
• Gasoline is highly FLAMMABLE and its vapors are EXPLO-
SIVE. Do not permit smoking, open flames, sparks or heat
in the area while handling gasoline. Avoid spilling gasoline
on a hot engine. Comply with all of the laws regulating
storage and handling of gasoline.
• Store gasoline and other fuels only in containers designed
and approved for the storage of such materials.
• Add gasoline in a clean, well-ventilated area. Wipe up any
spilled gasoline immediately. If gasoline has been spilled,
let it dry completely before starting the engine.
• Do not overfill the fuel tank. Always allow room for fuel
expansion. If the tank is overfilled, the fuel can overflow
onto a hot engine and cause a FIRE or an EXPLOSION.
• Allow at least two (2) feet of clearance on all sides of the
engine, even while operating it outdoors, or you could
damage the engine.
• Thoroughly inspect the engine for loose or damaged parts
before each use. Do not use the engine until adjustments
or repairs are made.
• Check the oil level in the engine before each use.
2
RULES FOR SAFE OPERATION
3
RULES FOR SAFE OPERATION
• Inspect the engine periodically. Repair or replace all damaged
or defective parts immediately.
• Inspect fuel system frequently for leaks or damage. Repair
or replace any damaged or leaking component immediately.
Never attempt to change, alter or modify the engine fuel
system in any way that might affect safety or compliance with
applicable codes and standards.
WHILE OPERATING
• This engine was designed and manufactured for specific
applications. Do not attempt to modify the equipment or use
it for any application for which it was not designed.
• Generac Power Systems does not approve or authorize the
use of these engines on All Terrain Vehicles (ATV’s), go-carts,
motorbikes, aircraft products, personal watercraft, or vehicles intended for use in competitive events. Use of these
engines in such applications could result in property damage,
serious injury (including paralysis), or even death.
• Engine exhaust gases contain DEADLY carbon monoxide
gas. This dangerous gas, if breathed in sufficient concentrations, can cause unconsciousness or even death. Operate
this equipment only in the open air where adequate ventilation is available.
• Do not insert any object through the cooling slots of the
engine. You could damage the equipment or injure yourself.
• Do not operate the engine faster than the speed necessary
to operate the equipment. Do not run the engine at high
speed when not operating the equipment.
• This engine requires an adequate flow of cooling air for its
continued proper operation. Never operate the equipment
inside any room or enclosure where the free flow of cooling air into and out of the equipment might be obstructed.
Without sufficient cooling air flow, the engine quickly overheats, damaging the engine or nearby property.
• Do not smoke around the engine. Wipe up any fuel or oil
spills immediately. Never leave oily or fuel soaked rags around
the engine. Keep the area around the engine clean and free
of debris.
• Keep hands, feet, clothing, etc., away from moving parts of
this engine.
• Never operate the engine (a) in the rain; (b) in any enclosed
compartment; (c) if the engine speed changes; (d) if the
engine sparks; (e) if flame or smoke is observed while the
engine is running.
• Never work on this engine or handle any electrical device
while standing in water, while barefoot, or while hands or
feet are wet. DANGEROUS ELECTRIC SHOCK will result.
SERVICE INFORMATION
Service on this engine within and after the warranty
period can be performed by any authorized service
dealer. Service technicians are factory trained and
capable of handling all service needs.
When contacting an authorized service dealer about
parts and service,
always supply the complete
model number and serial number of your unit as
given on its data plate decal. See the illustration
below for the location of the decal.
The warranty for this engine is included in the
owner’s manual.
The engine exhaust from this product contains
chemicals known to the State of California to
cause cancer, birth defects, or other repro-
ductive harm.
WARNING:
4
DIMENSIONS AND FEATURES
5
DIMENSIONS AND FEATURES
6
DIMENSIONS AND FEATURES
7
DIMENSIONS AND FEATURES
8
4-CYCLE ENGINE THEORY
If the engine is to run properly, four (4) events must occur in
the proper sequence and at the correct time. These events are
(a) intake, (b) compression, (c) ignition and power, and (d)
exhaust.
A INTAKE
The piston is travelling from top dead center (TDC) to bottom
dead center (BDC). The cam has opened the intake valve. The
piston's downward movement in the cylinder creates a partial
vacuum in the cylinder. Air at atmospheric pressure is drawn
into the cylinder through the carburetor and is mixed with fuel
in the carburetor. The fuel-air mixture flows through the open
intake valve into the cylinder. When the piston reaches BDC,
the intake stroke is over.
B COMPRESSION
As the piston reaches bottom dead center (BDC), both the
intake and exhaust valves are closed. The piston moves upward
toward TDC and the fuel-air mixture is compressed. Just before
the piston reaches TDC, ignition occurs.
C
IGNITION AND
POWER
By the time the piston reaches TDC , combustion is already
in progress. The intake and exhaust valves remain closed as the
expanding gases of combustion force the piston downward.
D EXHAUST
The exhaust stroke begins when the piston has reached BDC
and has started its upward movement. The intake valve is
closed. The exhaust valve is open to let gases escape.
1-1
SECTION 1: GENERAL INFORMATION
SECTION CONTENTS
PAGE
MAINTENANCE SCHEDULE ........................................... 1-1
FUEL AND OIL RECOMMENDATIONS.............................. 1-1
Gasoline .................................................................. 1-1
Lubrication ................................................................ 1-1
Recommended Oil Type.............................................. 1-1
Change Oil ................................................................ 1-2
Change Oil Filter........................................................ 1-2
Cleaning Intake Screen .............................................. 1-2
Replace Spark Plugs .................................................. 1-3
Air Cleaner Maintenance .......................................... 1-3
Service Dual Element Air Cleaners .............................. 1-3
Service Canister Air Cleaners...................................... 1-3
TROUBLESHOOTING ..................................................... 1-3
Systematic Check ...................................................... 1-4
Check Ignition .......................................................... 1-4
Check Ignition (Engine Running) ................................ 1-4
Check Ignition (Fouled Plug or Other Causes) ............ 1-4
Cylinder Balance Test ................................................ 1-4
Check Fuel ................................................................ 1-5
Check Compression....................................................1-5
Cylinder Leakdown Test ............................................ 1-5
Things Which Affect Both Cylinders .......................... 1-5
Things Which Affect One Cylinder ............................ 1-5
EQUIPMENT AFFECTING ENGINE OPERATION ................ 1-6
Hard Starting or Will Not Start .................................. 1-6
Engine Won’t Stop .................................................... 1-6
Vibration.................................................................... 1-6
Power Loss ................................................................ 1-6
Noise ........................................................................ 1-6
MAINTENANCE SCHEDULE
Every Every Every Every
8 Hours 25 Hours 50 Hours 100 Hours
or Daily Season Season Season
Check Oil Level •
Change Oil Note 1
Change Oil Filter Note 1
Foam Filter
Service Air Filter Pre-Filter (Note 2)
if equipped
Replace or Clean •
Spark Plug
Clean Spark •
Arrestor Screen
Adjust Valve Note 4
Clearance
Retorque Head Bolts Note 3
NOTE 1:
Change oil and filter after first 8 hours of operation and then
every 100 hours thereafter. Change sooner when operating under a heavy
load or in a dusty or dirty environment or in high ambient temperature.
NOTE 2:
Clean more often when operating in dirty or dusty conditions.
Replace canister style filter every 500 hours.
NOTE 3:
Perform this task ONLY after first 50 hours of operation. Head
bolts will NOT need further retorquing.
NOTE 4:
Check valve lash and adjust if necessary after first 50 hours of
operation and every 100 hours thereafter.
FUEL AND OIL RECOMMENDATIONS
GASOLINE:
We recommend the use of clean, fresh lead-free gasoline. A minimum of 85 octane is recommended. The use of lead-free gasoline
results in fewer combustion deposits and longer valve life.
NOTE: Using a fuel additive such as STA-BIL® fuel stabilizer, or an equivalent, will prevent gum deposits from
forming in the engine’s fuel system.
NOTE: Some fuels, called oxygenated or reformulated
gasolines, are gasolines blended with alcohols or ethers.
Excessive amounts of these blends can damage the fuel
system or cause performance problems. Do not use gasoline which contains Methanol. If any undesirable
operating symptoms occur, use gasoline with a lower percentage of alcohol or ether.
It is also recommended that gasoline be purchased in small
quantities, not more than a 30 day supply. FRESH gasoline minimizes gum deposits, and also will ensure fuel volatility tailored
for the season in which the engine will be operated.
LUBRICATION:
Oil has four purposes. It cools, cleans, seals and lubricates.
During normal operation, small particles of metal from the cylinder walls, pistons, bearings and combustion deposits will
gradually contaminate the oil. Dust particles from the air also
contaminate the oil forming an abrasive mixture which can
cause wear to all of the internal moving parts of the engine,
if the oil is not changed regularly. Fresh oil also assists in cooling. Old oil gradually becomes thick and loses its cooling ability
as well as its lubricating qualities.
RECOMMENDED OIL TYPE:
Using the proper type and weight of oil in the crankcase is
extremely important. Check the oil before each use and change
the oil regularly (see Figures 1-1, 1-2 & 1-3). Failure to use the
correct oil, or using dirty oil, can cause premature engine wear
and failure.
Use only high quality detergent oil rated with API service classification SF, SG or SH. The recommended oil weights include
the following:
1-2
SECTION 1: GENERAL INFORMATION
• During summer months: SAE 30. An acceptable substitute
is SAE 10W-30. After first oil change, synthetic oil is
acceptable.
• During winter months: SAE 5W-30, Synthetic 5W-20 or 5W-
30. DO NOT USE SAE 10W-40.
CHANGE OIL:
The crankcase oil capacity is about 2030 ml (2.1 qt.) with the
oil filter. Without the filter, the oil capacity is 1750 ml (1.8 qt.).
Use no special additives. Make sure that the unit is level when
filling with oil. DO NOT OVERFILL.
IMPORTANT: DO NOT OVERFILL. Check and maintain oil
level regularly. Change oil and filter after first eight (8)
hours of operation.
Thereafter, change oil and filter every 100 hours of operation. Change oil more often if engine is operated in dirty or
dusty conditions or if engine is operated under heavy loads or
in high ambient air temperatures.
Remove oil drain plug and drain oil while engine is still warm,
Figure 1-2. Change oil filter (Figure 1-3) and replace drain plug.
Figure 1-1. Oil Fill/Check
Remove dipstick and refill slowly with new oil of proper service classification and viscosity grade. Refill to full mark on
dipstick. When checking oil level, dipstick must be all the way
in for accurate readings.
Start and run engine to check for oil leaks.
CHANGE OIL FILTER:
Replace oil filter every 100 hours. Before installing new filter,
lightly oil filter gasket with fresh clean engine oil. Screw filter
on by hand until gasket contacts filter adapter. Tighten 3/4 to
one full turn farther, Figure 1-3.
Start and run engine at idle for 30 seconds and stop engine.
Recheck oil level and add if required. Restart engine and check
for oil leaks.
Figure 1-2. Oil Drain
Figure 1-3. Oil Filter
CLEANING INT
AKE SCREEN:
Grass particles, chaff or dirt can clog the air cooling system,
especially after prolonged service in cutting dry grass or when
operating in extremely dusty or dirty conditions. Continued
operation with a clogged cooling system can cause severe
overheating and possible engine damage. Figure 1-4 shows the
areas to be cleaned. This should be a regular maintenance operation, or clean intake screen and oil cooler fins after each use.
10W-30, SAE 30
Synthetic 5W-20, 5W-30
F
-20
C -30
0
-20
20
-10
Temperature Range of Expected Use
40
10
60
20
80
30
100
40
DRAIN
FILL / CHECK
FILTER
1-3
SECTION 1: GENERAL INFORMATION
Figure 1-4. Clean Intake Screen & Oil Cooler Fins
REPLACE SPARK PLUGS:
Replace spark plugs every 100 hours of operation or every
season, whichever occurs first. Replace spark plugs if electrodes are burned away, or the porcelain is cracked. Set spark
plug gap at .76 mm (.030") for all models. Torque spark plugs
to 20.0 Nm (180 in. lbs.).
Figure 1-5. Setting Spark Plug Gap
GENERAC Champion
Spark Plug Type Part No. Part No.
Resistor Plug 072347 RC12YC
AIR CLEANER MAINTENANCE:
WARNING: NEVER OPERATE ENGINE WITH AIR
CLEANER ASSEMBLY OR AIR CLEANER CARTRIDGE
REMOVED. FIRE MAY RESULT.
A properly serviced air cleaner protects internal parts of the
engine from dirt and dust particles in the air. If air cleaner instruc-
tions are not carefully followed, dirt and dust which should be
collected in the cleaner, will be drawn into the engine. These
particles are highly abrasive and will cause the piston rings and
cylinder bore to wear quickly. As the rings and cylinder bore
become worn, these abrasive particles enter the crankcase
and contaminate the oil, forming an abrasive mixture which
will cause wear on all of the internal moving parts.
The air cleaner on every engine brought in for a check up
or repair should be examined and serviced. If the air cleaner
shows signs of neglect, show it to the customer before cleaning. Instruct the customer on proper care, to assure long
engine life.
Note: Replace air cleaner gaskets and mounting gaskets
that are worn or damaged, to prevent dirt and dust from
entering engine due to improper sealing. Replace bent
air cleaner mounting bracket if necessary.
SERVICE DUAL ELEMENT AIR CLEANERS:
Remove and service foam pre-cleaner every 25 hours or every
season, whichever occurs first. Service cartridge every 50 hours
or every season, whichever occurs first.
SER
VICE CANISTER AIR CLEANERS:
Clean the air filter element(s) with compressed air every 50
hours or every season, whichever occurs first. Replace the air
filter element(s) every 500 hours or if damaged.
Note: The air cleaner assemblies on some equipment
may have been supplied by the equipment manufacturer. See the equipment manufacturer’s owner’s manual
for service information specific to that product.
TROUBLESHOOTING
Most complaints concerning engine operation can be classified as one or a combination of the following:
1. Will not start
2. Hard starting
3. Lack of power
4. Runs rough
5. Vibration
6. Overheating
7. High oil consumption
Note: What appears to be an engine malfunction may be
a fault of the powered equipment rather than the engine.
If equipment is suspect, see equipment affecting engine
operation.
INTAKE
SCREEN
OIL
COOLER
FINS
1-4
SECTION 1: GENERAL INFORMATION
SYSTEMATIC CHECK:
If the engine will not start and the cause of malfunction is
not readily apparent, perform a systematic check in the following
order:
1. Ignition
2. Fuel
3. Compression
This check-up, performed in a systematic manner, can usually be done in a matter of minutes. It is the quickest and surest
method of determining the cause of failure. The basic checkup
procedure is the same for all engine models, while any variation, by model, will be shown under the subject heading.
CHECK IGNITION:
If spark does not occur look for:
• Shorted ignition/kill wire
• Two closed diodes in ground wire harness
• Incorrect armature air gap
• Armature failure
CHECK IGNITION (ENGINE RUNNING):
If engine runs but misses during operation, a quick check to
determine if ignition is or is not at fault can be made by
installing a spark tester (Generac P/N OC5969) between the
spark plug lead and each spark plug, Figure 1-6. A spark miss
will be readily apparent when the engine is running. If spark
is good but engine misses, check for a fouled spark plug.
Figure 1-6. Running Check
CHECK IGNITION (FOULED PLUG OR OTHER CAUSES):
To check for a fouled spark plug or a non-functioning cylinder, attach the spark tester (Generac P/N OC5969) between the
spark plug lead and each spark plug. Start and run engine at
top no load speed. Now ground one spark plug, Figure 1-7. The
engine should continue to run on the other cylinder. Repeat this
test with the other cylinder. If the engine will not continue to
run when making this test, the cylinder that is NOT grounded
is not functioning and/or the spark plug is fouled. Install a new
spark plug before proceeding. If miss continues, problem may
be carburetion or compression. See Check Carburetion, Check
Compression. Also see Cylinder Balance Test.
Figure 1-7. Checking For Fouled Plugs
CYLINDER BALANCE TEST
:
If the engine is hard starting, runs rough, misses or lacks
power, perform a cylinder balance test to determine whether
both cylinders are operating to their full potential.
Tools Required:
1. Two Ignition Testers (Generac P/N OC5969)
Attach an ignition tester between the spark plug lead and
each spark plug, Figure 1-6.
Start and run engine running at top no load speed and note
spark at ignition testers. If the spark is equal at both ignition
testers, the problem is not ignition related. A spark miss will
be readily apparent. Now note RPM of engine. Ground out one
cylinder by contacting ignition tester and a good ground on
engine, Figure1-8. Note RPM loss. Then ground out the other
spark plug and note the RPM loss. If the difference between
the two cylinders does not exceed 75 RPM, the amount of work
the two cylinders are doing should be considered equal.
SPARK
PLUG
LEAD
TESTER
SPARK PLUG
1-5
SECTION 1: GENERAL INFORMATION
If the RPM loss is greater than 75 RPM this indicates that the
grounded cylinder with the least RPM loss is the weakest of
the two cylinders. Look to that cylinder for a problem.
Example:
Engine RPM - Both Cylinders = 3400 RPM
Engine RPM - #1 Cylinder Grounded = 3300 RPM
Engine RPM - #2 Cylinder Grounded = 3100 RPM
Conclusion: #1 cylinder is weakest of the two cylinders.
Figure 1-8. Cylinder Balance Test
The cylinder balance test will also detect a cylinder that is not
functioning. When grounding out one cylinder there will be
no RPM loss. When the other cylinder is grounded out the
engine will stop.
CHECK FUEL:
The fuel pressure can be checked using a pressure tester kit
for LP and NG systems.
CHECK COMPRESSION:
It has been determined through testing that a simple and accurate indication of compression can be made as follows:
Remove both spark plugs and insert a compression gauge into
either cylinder (one cylinder at a time). Turn engine over with
engine starter until there is no further increase in pressure.
Record this reading. Repeat procedure on other cylinder and
record that reading. The difference between both cylinders
should not exceed 25%. More than 25% indicates loss of compression in the cylinder with lower pressure. See example.
EXAMPLE:
Cyl. #1 Cyl. #2 Diff.
Eng. #1 165 PSI 160 PSI 5 PSI
Eng. #2 175 PSI 155 PSI 20 PSI
If compression is poor, look for:
• Insufficient valve clearance
• Loose cylinder head bolts
• Blown head gasket
• Burned valves, valve seats and/or loose valve seats
• Warped cylinder head
• Warped valve stems
• Worn bore and/or rings
• Broken connecting rods
CYLINDER LEAKDOWN TEST
:
A cylinder leakdown tester may be used to test the sealing
capability of the compression components of each cylinder and
quickly identify the problem component.
THINGS WHICH AFFECT BOTH CYLINDERS:
1. Carburetion
2. Crankcase vacuum
3. Ignition timing
a. A partially sheared flywheel key will effect ignition timing
and engine performance.
THINGS WHICH AFFECT ONE CYLINDER:
1. Spark plug
a. A fouled spark plug may indicate that carburetor is out
of adjustment.
2. Leak in spark plug wire
3. Head gasket
4. Intake manifold
a. A leak at either end of the intake manifold will only affect
one cylinder, not both.
5. Valves
6. Rings
7. Piston
8. Cylinder
NOTE: A twin cylinder engine will run well on one cylinder as long as the power required for the application does
not exceed the power produced by the one cylinder.
1-6
SECTION 1: GENERAL INFORMATION
EQUIPMENT AFFECTING ENGINE OPERATION
Frequently, what appears to be a problem with engine operation, such as hard starting, vibration, etc., may be the fault
of the equipment powered rather than the engine itself. Listed
are the most common effects of equipment problems, and what
to look for as the most common cause.
HARD STARTING OR WILL NOT ST
ART:
1. Loose belt - a loose belt like a loose blade can cause a back-
lash effect, which will counteract engine cranking effort.
2. Starting under load - see if the unit is disengaged when
engine is started; or if engaged, should not have a heavy
starting load.
3. Check remote control assembly for proper adjustment.
4. Check interlock system for shorted wires, loose or corroded
connections, or defective modules or switches.
ENGINE WON'T STOP:
1. Check equipment ignition stop switch.
2. Check for loose or disconnected equipment stop switch
wire.
3. Check ground wire harness on engine.
a. See Section 2 for test procedure.
VIBRATION:
1. Unit load out of balance - remove and balance.
2. Mounting bolts loose - tighten.
POWER LOSS:
1. Bind or drag in unit- if possible, disengage engine and oper-
ate unit manually to feel for any binding action.
2. Unit load has excess drag.
NOISE:
1. Engine coupling or pulley - an oversize or worn coupling
can result in knocking, usually under acceleration. Check
for fit or tightness.
2. Equipment needs lubrication.
2-1
SECTION 2: IGNITION
SECTION CONTENTS
PAGE
SPECIFICATIONS............................................................. 2-1
GENERAL INFORMATION................................................ 2-1
ARMATURES
Armature Testing ...................................................... 2-1
Removing Armatures ................................................ 2-1
Install Armatures........................................................ 2-1
Adjust Armature Air Gap .......................................... 2-2
FLYWHEEL
Remove Flywheel ...................................................... 2-2
Inspect Flywheel Key and Keyways ............................ 2-2
Install Flywheel .......................................................... 2-3
ENGINE WIRING HARNESS ............................................2-3
Testing Ground Wires ................................................ 2-3
Engine Wiring Harness Diagram ................................ 2-4
Diode Failure Diagnosis ............................................ 2-4
SPECIFICATIONS FOR
GTV-990/760 OHVI V-TWIN ENGINE
MODEL SERIES................................................ GTV-990/760
ARMATURE AIR GAP .............................. 0.20 TO 0.30 MM
(0.008" TO 0.012")
FLYWHEEL NUT TORQUE
FT. LBS. ........................................................................ 150
FLYWHEEL NUT TORQUE
NM .............................................................................. 203
See Section 1 For Spark Plug Maintenance And Specifications
GENERAL INFORMATION
Generac GTV-990/760 OHVI V-Twin engines use a magneto
ignition: an ignition armature with a self-contained transistor
module (no moving parts). Two magneto ignition armatures
are used, with a flywheel containing a permanent magnet.
NOTE: The magneto ignition system requires a minimum
of 250 RPM to produce a consistent spark.
ARMATURES
ARMATURE TESTING:
The condition of the ignition armatures can be accurately diagnosed using an ignition tester, (Generac P/N 0C5969) as
described in "Troubleshooting" in Section 1.
REMOVING ARMATURES:
1. Remove spark plug leads.
2. Remove intake manifold and cover intake ports.
3. Remove rotating screen and blower housing.
4. Remove armature screws and lift off armature(s),
Figure 2-1.
a. Disconnect stop switch wires at armatures.
Note:The flywheel does not need to be removed to service ignition except to check the flywheel key.
Figure 2-1. Removing Armature
INST
ALL ARMATURES:
1. Turn flywheel so magnet is away from armature.
2. Install ground wire onto tab terminal on armature.
Note: Make sure wires are routed over armature mounting posts and away from flywheel.
Figure 2-2. Installing Armature
3. Assemble armature to engine, Figure 2-2.
a. Mounting holes in armature are slotted. Push armature
away from flywheel as far as possible and tighten one screw
to hold armature in place.
2-2
SECTION 2: IGNITION
4. Repeat for second armature.
5. Adjust armature air gap.
ADJUST ARMATURE AIR GAP:
1. Rotate flywheel until magnet is under armature
laminations.
2. Place thickness gauge, 0.20-.30 mm (.008"-.012") between
magnet and armature laminations, Figure 2-3.
3. Loosen mounting screw so magnet will pull armature down
against thickness gauge.
a. Torque screws to 12.2 Nm (9 ft. Ibs.).
4. Rotate flywheel to remove thickness gauge.
5. Repeat for second armature.
Note: Route armature ground wire over breather tube
and away from the flywheel.
Figure 2-3. Adjusting Air Gap
FLYWHEEL
REMOVE FLYWHEEL:
1. Remove flywheel nut and washer, Figure 2-4.
2. Remove fan retainer and fan.
4. Reinstall flywheel nut. Turn nut down flush with top of
threads.
5. Install flywheel puller.
6. Tighten puller screws equally until flywheel loosens,
Figure 2-5.
Figure 2-4. Removing Flywheel Nut
Caution: Flywheel puller bolts may damage lighting
coil if turned in too far.
Caution: DO NOT strike flywheel with a hard object
or a metal tool as this may cause flywheel to shatter in operation. Always use approved flywheel
removal tools.
Figure 2-5. Removing Flywheel
INSPECT FL
YWHEEL KEY, KEYWAYS, FLYWHEEL AND
CRANKSHAFT:
Check flywheel key for damage. Check flywheel for cracks
or keyway damage. Also check crankshaft keyways and taper
for damage, Figure 2-6. Replace crankshaft, if damaged.
!
!
2-3
SECTION 2: IGNITION
Figure 2-6. Check Flywheel And Crankshaft
INST
ALL FLYWHEEL:
Note: CLEAN flywheel and crankshaft taper removing all
oil, dirt or grease.
1. Insert flywheel key into crankshaft.
2. Align keyways and assemble flywheel to crankshaft.
3. Install washer and flywheel nut.
a. Torque flywheel nut to 204.0 Nm (150 ft. Ibs.), Figure 2-7.
4. Assemble fan and retainer to flywheel, Figure 2-8.
a. Torque screws to 21.7 Nm (192 in. Ibs.).
Figure 2-7. Torquing Flywheel Nut
Figure 2-8. Installing Flywheel And Fan
ENGINE WIRING HARNESS
The engine wiring harness consists of a ground wire with a
diode for each armature and a separate wire for the carburetor
solenoid. The engine kill wires are connected to the wiring harness provided by the equipment manufacturer.
See “Typical 12 Volt Wiring Diagram”, Page 6-3.
TESTING GROUND WIRES:
Use a Digital Multimeter (Figure 2-9) to test the ground
wires.
The following test will be made with the meter in the Diode Test
position.
In the Diode Test position, the meter will display the forward
voltage drop across the diode(s). If the voltage drop is less than
0.7 volts, the meter will "Beep" once as well as display the voltage drop. A continuous tone indicates continuity (shorted diode)
An incomplete circuit (open diode) will be displayed as "OL."
Figure 2-9. Digital Multimeter
2-4
SECTION 2: IGNITION
1. Insert RED test lead into receptacle in meter.
2. Insert BLACK test lead into the “COM” receptacle in meter.
3. Rotate selector to (Diode Test) position.
4. Insert RED test lead clip into connector "A" (Figure 2-10).
Leave attached for remainder of test.
5. Touch BLACK test lead probe to terminal "B."
a. If meter "Beeps" once, diode is OK.
b. If meter makes a continuous tone, diode is defective
(shorted). Replace ground harness.
c. If meter displays "OL," diode is defective (open). Replace
ground harness.
6. Now repeat test for terminal "C." Results must be the same.
See “Diode Failure Diagnosis” below.
Figure 2-10. Testing Ground Wire
SWITCH ON TURNED OFF CAUSE
Engine Runs Shuts Off OK 1 Closed Diode
On 1 Cylinder
Engine Runs Only One Cylinder 1 Open Diode
(Both Cylinders) Shuts Off
Won't Run 2 Closed Diodes
(No Spark)
Engine Runs Engine Won't Shut Off 2 Open Diodes
(Both Cylinders)
Figure 2-11. Engine Wiring Harness
DIODE FAILURE DIAGNOSIS
ENGINE
GROUND
HARNESS
A
POSITIVE METER
TEST LEAD
C
B
NEGATIVE METER
TEST LEAD
IGNITION KILL WIRE
3-1
SECTION CONTENTS
PAGE
CARBURETOR TYPES ..................................................... 3-1
CARBURETOR REMOVAL................................................ 3-1
CLEANING CARBURETOR .............................................. 3-1
CARBURETOR INSTALLATION ........................................ 3-2
STATIC GOVERNOR ADJUSTMENT.................................. 3-2
FUEL PUMP .................................................................... 3-3
CARBURETOR TYPES
There are four types of carburetors used on Generac OHVI
V-twin engines:
1. Keihin two-barrel, side-draft on Models EVT-04198-0, EVT04629-0, EVT-04629-1, EVT-04630-0, EVT-04741-0,
EVT-04772-0, EVT-04797-0, 04807-0, 04861-0, 0D3358,
0E0038.
2. Deni two-barrel, side draft on Models EVT-04174-0, 041981, 04629-2, 04806-0, 0E3342.
3. Nikki two-barrel, side-draft on Models EVT-04712-0, EVT04717-0, 04717-1, EVT-04739-0, 04857-0, 04858-0,
04862-0, 0D7675, 0D9033.
4. Nikki single-barrel, side-draft on Model 0D9708.
CARBURETOR REMOVAL - VERTICAL SHAFT
(Models EVT-04629-0, EVT-04629-1, 04629-2, EVT-04717-0,
04717-1, EVT-04797-0, 04806-0, 04857-0, 04858-0, 04862-0,
04861-0)
1. Unclip choke link from bellcrank and remove link from
carburetor.
2. Disconnect fuel-shutoff solenoid by unbolting the ground
wire from the manifold, and unplugging the power wire.
Note: Wires simply unplug from the solenoid on models
04629-2, EVT-04717-0, 04717-1, 04806-0, 04857-0, 048580, & 04862-0.
3. Disconnect breather tube.
4. Separate throttle link balljoint from carburetor by rotating
the ball socket.
5. Disconnect the fuel line.
6. Remove the four nuts holding the carburetor and plenum
to the intake manifold.
7. Remove the plenum, carburetor, and gaskets from the
manifold, and discard the gaskets.
Figure 3-1.
Figure 3-2.
CLEANING CARBURETOR
For cleaning purposes, the carburetor's float bowl may be
removed. It is recommended that all jetting be left in place while
cleaning the carburetor. Be sure to use a cleaner that won't
damage rubber, neoprene, or plastic parts.
If the fuel-shutoff solenoid is suspected of being faulty, it is
replaceable by simply unthreading it from the float bowl, and
installing a new one in its place. It can be checked by applying 12 volts to it. If you hear it click, it is most likely working
properly. If there is anything else wrong with the carburetor,
it is recommended that the entire carburetor be replaced with
a new one.
SECTION 3: CARBURETION
3-2
SECTION 3: CARBURETION
CARBURETOR INSTALLATION - VERTICAL SHAFT
(Models EVT-04629-0, EVT-04629-1, 04629-2, EVT-04717-0,
04717-1, EVT-04797-0, 04806-0, 04857-0, 04858-0, 04862-0,
04861-0)
1. Slide new carburetor gasket onto the studs.
2. Slide the carburetor onto the studs.
3. Slide new plenum gasket onto the studs.
4. Slide the plenum onto the studs.
5. Install the nuts on the four studs, and torque to 5.4 Nm
(4 ft. lbs.).
6. Connect the fuel line.
7. Using a pliers, reassemble the balljoint on the carburetor.
8. Connect the breather tube.
9. Connect the fuel-shutoff solenoid.
Figure 3-3.
10. Reinstall choke link in carburetor and clip the link into the
bellcrank.
11. Perform a static governor adjustment.
12. Start engine and allow to warm up for 5 minutes.
13. Move speed control lever to slow speed position and hold
throttle lever against idle stop screw.
14. Adjust stop screw to maintain ~1200 RPM idle.
15. Slowly move speed control lever to high speed position.
Do not exceed 4000 RPM.
Figure 3-4.
Note: The high speed screw may need adjusting to reach
the speed control stop without exceeding 4000 RPM.
16. With the speed control in the high speed position, adjust
the high speed screw to obtain the desired engine speed.
Figure 3.5.
STATIC GOVERNOR ADJUSTMENT
1. Loosen the clinching screw on the governor lever.
2. Hold governor lever in WOT position and rotate the governor arm clockwise.
3. While holding this position, re-torque the clinching screw
to 11.3 Nm (100 in-lbs.).
4. Check to make sure that the throttle travels from WOT to
IDLE. If it doesn't, the governor needs to be reset again.
MANIFOLD
PLENUM
PLENUM
GASKET
CARBURETOR
GASKET
IDLE
CLINCHING
SCREW
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