CARBURETION
3.31
Troubleshooting
Fuel system diagnosis should follow a specific path, first examining the fuel tank, then the filters, fuel lines, vent
lines, fuel pump, impulse hose, air box, exhaust system and finally the carburetors.
The following troubleshooting information assumes that the general mechanical condition of the engine (pistons,
rings, bearings, etc.) is good.
When the fuel/air mixture is diagnosed as improper due to spark plug readings, clean the carburetor and blow
its passages clear with compressed air. Use the spark plug firing end condition as a guide for further determination
of whether the mixture is too rich or too lean.
Use the throttle lever to determine at what degree of throttle valve opening the problem exists.
CONDITION
SYMPTOMS
Mixture Too Rich -Black spark plug tip
-Heavy exhaust smoke
-Engine runs worse after warm up
-Runs better without air silencer
-Combustion chamber has heavy deposits of carbon
Mixture Too Lean -Spark plug electrodes white
-Fluctuation in engine speed
-Power loss
-Engine overheats
-Cylinder scoring
-Backfiring - detonation
-Throttle diagnostic opening check points
Poor Fuel Mileage -Incorrect ignition timing
-Improper track tension (too tight)
-Incorrect carburetor jetting
-Fuel leaks (lines, fittings, fuel pump)
-Needle and seat leaks
-Plugged exhaust
-Carburetor vent line problems
-Clutching incorrect for conditions
Troubleshooting Tips, 0-1/4 Throttle:
S Pilot air screw mis-adjusted
S Pilot jet of wrong size
S Obstruction of pilot jet
S Pilot jet loose
S Choke plunger not seating (rich)
S Carburetor mounting air leak (lean)
S Crankshaft seal air leak (lean)
S Fuel pump diaphragm damaged (rich)
S Float level incorrect
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