Maintenance
2.38
General Troubleshooting -- Continued
Rich Fuel Mixture
Symptoms: Fouled spark plugs; black sooty exhaust; rough idle, idle unstable; poor fuel economy; rough running
(four cycling); misses; poor performance; bogs; loads up; backfires (plug fouling).
S Thermostat/pop--off leak, dirty or damaged
S Carburetor mixture needles damaged or adjusted incorrectly
S Needle and seat damaged
S Misuse of choke
S Fouled spark plugs
S Fuel pump diaphragm damaged (ruptured)
S Carburetor synchronization incorrect
S Needle and seat control arm too high or sticking
S Collapsed exhaust hose or pipe (restricted)
S Air intake restricted
S Broken, cracked or poorly sealing reed valve
S Low compression
S Ignition problem
S Anti-siphon valve worn or broken
S Exhaust hose delaminating present.
Symptoms: Engine backfires.
S Weak spark from fouled, defective, worn or wrong spark plugs
S Broken reed petals
Symptoms: Engine “pinging” or “knocking”.
S Lean fuel mixture
S Poor quality, low octane gasoline
S Incorrect ignition timing
S Spark plug heat range too high
Symptoms: Engine power loss.
S Weak spark
S Incorrect fuel or fuel mixture
S Water in fuel system or oil tank
S Fuel filter restricted
S Jet intake clogged
S Cooling system clogged
Symptoms: Engine noise.
S Detonation (see causes for holed or eroded pistons, this section)
S Excessive piston clearance
S Exhaust leak, loose exhaust pipe or muffler (water box)
S Engine mounts or mount plate loose or rubber mounts broken
S Drive coupler splines dry
S Driveshaft runout excessive
S Driveshaft end play incorrect; rubber dampers worn or missing
S Broken ring or ring land
S Oil pump bushing end play excessive
S Ignition timing incorrect
S Piston pin damaged or bent
S Connecting rod bearing failure (small end or big end)Crankshaft main bearing failure or wear
Flywheel loose
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