Tecumseh OHH50 - 65 Handbook page 65

ENGINE MISFIRES
Carburetor improperly adjusted
Wrong or fouled spark plug
Valves sticking or not seating properly
Ignition timing or
incorrect spark plug
Excessive carbon build up
Improper Valve Lash
Weak valve spring
ENGINE OPERATION PROBLEMS
ENGINE VIBRATES EXCESSIVELY
Bent crankshaft
Attached equipment out of balance
Loose mounting bolts
If applicable counter balance not
properly aligned
LACKS POWER
Air intake obstructed
Lack or lubrication or improper
lubrication
Carburetor improperly adjusted
Exhaust Obstructed
Improper valve lash
Loss of compression (worn rings,
blown head gasket)
BREATHER PASSING OIL
Oil level too high
Excessive RPM or improper governor
setting
Damaged gaskets, seals or "O" rings
Breather damaged, dirty or improperly
installed
Piston rings not properly seated or ring
end gaps are aligned
Angle of operation too severe