What Makes a Troy-Bilt Riding Mower Smoke?

Engine Tilting

• A common cause for smoke to come from a mower engine is tilting the engine too far off level. Tilting the mower too far, such as on a steep slope or when working on the mower, can force oil from the oil tank into other engine parts like the crankcase, combustion chamber, air filter or exhaust manifold. This will cause the engine to smoke when the engine is running. Often this condition will improve as the oil burns off, but it can cause engine failure, too.

Combustion Chamber

• If your Troy-Bilt's engine leaks oil, as often is the case as a small engine wears. If the leak penetrates the combustion chamber, the oil will burn in the combustion chamber along with the gasoline and air, and it will cause a more visible smoke than an engine burning just gas and air. Leaks can also foul the engine's spark plug, which also will cause a bit of smoke.

Fuel Mixture

• Whether they are riding mowers or push mowers, all gas-powered Troy-Bilt mowers use carburetors to mix fuel and air for combustion. Some models, like the Thoroughbred riding mower, have an engine choke mechanism that allows you to adjust the fuel mix. If the mix is too rich, the mower will emit smoke. Fuel that sits too long in the tank or lines (such as during the off-season) can cause the engine to emit smoke, too.

Air Filter

• Air filters on Troy-Bilt riding mowers help keep the engine free of debris and provide an inlet for clean air to the carburetor. If the air filter is clogged the engine may smoke. The crankcase breather lets air escape the crankcase in a controlled manner and allows clean air into the crankcase. It also filters out oil mist. If oil leaks into the breather or the crankcase breather fails, it can cause a clog that turns into black smoke.

Broken Seals

• Broken seals and gaskets also cause mowers to smoke. A broken diaphragm gasket in the carburetor allows too much fuel into the combustion chamber. Broken piston parts like cylinders, rings and gaskets will leak fuel into the exhaust or muffler, causing smoking.