G424 Service Manual Adjustment and Troubleshooting185
Problem Probable Cause Probable Solution
Carburetor Backfire Incorrect full load air/fuel duty Verify full load air/fuel duty
cycle
Faulty vapor connection Check connection
between pressure regulator • No holes in hose
and carburetor • Clamps must be tight
• Watch for kinked and/or pinched and/or
collapsed hose
Ignition malfunction Check ignition system, repair/replace
Incorrect ignition timing Check ignition timing
setting • Measure initial timing
• Measure centrifugal timing advance
Engine mechanical See Troubleshooting section
Poor High Speed Clogged fuel filter Repair/replace as required
Performance/Lean • Close liquid fuel valve
Condition • Using caution, disconnect fuel line
• Remove/replace filter element
• Clean fuel filter housing
• Open liquid fuel valve
• Leak test
Plugged fuel line Remove obstruction from fuel line
• Close liquid fuel valve
• Using caution, disconnect fuel line
• Clear obstruction with compressed air
• Re-connect fuel line
• Leak test
Faulty vapor connection Check connection
between pressure regulator • No holes in hose
and carburetor • Clamps must be tight
• Watch for kinked and/or pinched and/or
collapsed hose
Throttle butterfly not opening Verify wide open throttle
Incorrect full load air/fuel duty Verify full load air/fuel duty cycle
cycle
Carburetor malfunction Check carburetor
• Remove air/gas valve assembly
• Clean air/gas valve and carb throat
• Check diaphragm for holes/damage
• Check air/gas valve for wear/damage
• Repair/replace as required
Pressure regulator Test pressure regulator operation
malfunction • Use test kit
• Install primary pressure gauge
• Install secondary pressure gauge
• Crank engine and observe readings on
pressure gauges
• Compare readings to specifications
• If readings are out of spec repair/replace
pressure regulator
Incorrect ignition timing Check ignition timing
setting • Measure initial timing
• Measure centrifugal timing advance
Air filter clogged Check air filter
• Clean/replace as required
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