White smoke
- Piston oil ring worn. The ring may be broken or damaged, causing oil from the crankcase to be pulled past the piston into the combustion chamber. Replace the rings with new ones (Chapter 2).
- Cylinders worn, cracked, or scored. Caused by overheating or oil starvation. Check the cylinder bores, lubrication system and cooling system (see Chapters 2 and 3).
- Valve stem oil seal damaged or worn. Replace oil seals with new ones (Chapter 2).
- Valve guide worn. Perform a complete valve job (Chapter 2).
- Engine oil level too high, which causes the oil to be forced past the rings. Drain oil to the proper level (Chapter 1).
- Head gasket broken between oil return and cylinder. Causes oil to be pulled into the combustion chamber. Replace the head gasket and check the head for warpage (Chapter 2).
- Abnormal crankcase pressurisation, which forces oil past the rings. Clogged breather is usually the cause.
Black smoke
- Air filter clogged. Clean or replace the element (Chapter 1).
- Main jet too large or loose. Compare the jet size to the Specifications (Chapter 4).
- Choke cable or plungers stuck, causing fuel to be pulled through choke circuit (Chapter 4).
- Fuel level too high. Check and adjust the float height(s) as necessary (Chapter 4).
- Float needle valve held off needle seat. Clean the float chambers and fuel line and replace the needles and seats if necessary (Chapter 4).
Brown smoke
- Main jet too small or clogged. Lean condition caused by wrong size main jet or by a restricted orifice. Clean float chambers and lets and compare jet size to Specifications (Chapter 4).
- Fuel flow insufficient - float needle valve stuck closed due to chemical reaction with old fuel: fuel level incorrect; restricted fuel line; faulty fuel pump (Chapter 4).
- Carburettor intake manifold clamps loose (Chapter 4).
- Air filter poorly sealed or not installed (Chapter 1).