Engine fails to start or is difficult to start—possible cause may be :-
- Throttle opened too far.
- If cold, air lever in open position, or bad air leak at carburetter flange.
- If cold, lack of fuel due to insufficient flooding of carburetter.
- Lack of fuel due to stoppage in pipe, taps, or air lock in tank.
- If engine hot, excessive flooding of carburetter.
- Carburetter pilot system choked.
- Sparking plug H.T. lead come adrift.
- Sparking plug dirty or oiled up.
- Sparking plug gap incorrectly set.
- Sparking plug external insulator dirty or damp.
- Sticking valves.
- Broken valve spring.
- Valves not seating properly.
- Contact points dirty or incorrectly adjusted.
- Dirty or wet high tension brush holder and lead.
- Dirty slip ring or stuck pick-up brush.
Engine misfiring—possible cause may be :-
- Air valve not opened fully.
- Defective or oiled up sparking plug.
- Contact breaker incorrectly adjusted or points loose.
- Tappet clearance incorrect.
- Contact breaker points dirty or oily.
- Valve springs weak.
- Fuel supply restricted due to blockage.
- High tension lead to plug faulty or insecurely fitted to magneto or suppressor.
- Carburetter float punctured.
Loss of power—possible cause may be :-
- Sparking plug faulty or unsuitable type.
- Insufficient oil in tank, or dirty or unsuitable oil.
- Oil pump not primed.
- Valve springs weak or broken.
- Valves sticking or not seating properly.
- Valve or ignition timing incorrect.
- Piston rings worn or broken.
- Engine excessively carboned.
- Brakes sticking on or too closely adjusted.
- Silencer tampered with.
Engine overheating—possible cause may be :-
- Faulty lubrication. Insufficient, dirty, or unsuitable oil.
- Oil pump not primed.
- Sparking plug faulty or unsuitable type.
- Air valve not opened fully.
- Carburetter float punctured.
- Engine excessively carboned.
- Valve springs weak or broken.
- Valves sticking, or not seating properly.
- Piston rings worn or broken.
- Valve or ignition timing incorrect.
- Brakes sticking on or too closely adjusted.
Engine stops suddenly—possible cause may be :-
- Lack of fuel in tank or supply obstructed.
- High tension lead come adrift.
- Carburetter choked.
- Carburetter float chamber air locked due to choked vent.
- Fuel tank air locked due to choked vent in cap.
- Sparking plug oiled up, or points bridged.
- Water on high tension pick-up or sparking plug.
- Water in float chamber.
Excessive oil consumption—possible cause may be :-
- Suction filter in crankcase restricted.
- Fabric oil filter element requires replacing.
- Air leak into crankcase at bottom.
- Ball valve leaking.
- Cylinder, piston, and rings worn.
Excessive fuel consumption —possible cause may be :-
- Fuel taps, pipe, or unions leaking.
- Level too high in carburetter.
- Punctured float.
- Incorrect use of air lever.
- Needle jet worn.
- Needle incorrectly set.
- Pilot air adjustment too rich.
- Valve or ignition timing incorrect.
- Brakes sticking on or too closely adjusted.