While regular maintenance on lawn tractors can help prevent problems, many things still can go wrong. Some common signs of trouble with lawn tractors are smoking, leaking fuel, unusual noises and vibrations. Most things that go wrong are easy to identify and correct.
Produces White, Blue or Gray Smoke
An oil leak or spill is the most common reason for a lawn tractor to produce white, blue or gray smoke. Oil leaks occur around worn crankcase gaskets and seals and worn valve stems, guides and seals. Worn or damaged oil rings or cylinder bores also leak oil.
Excess oil from the oil reservoir can drip onto the engine and smoke when the engine gets hot. If the lawn tractor is tipped on its side, oil can run into the combustion chamber, carburetor or exhaust system and make smoke when it heats up. Using oil contaminated with water or gas, or using the wrong type of fuel, can also produce white, blue or gray smoke.
Produces Black Smoke
A lawn tractor produces black smoke when it is using a rich fuel mixture or when it is not completely using the normal amount of fuel. Dirty or worn spark plugs and clogged air filters are common causes of black smoke. Trash in the fuel system can interfere with the proper flow of gas and cause black smoke. A carburetor that is not adjusted properly allows too much gas to flow through and produces black smoke.
If a lawn tractor uses too much fuel or leaks fuel, the engine may need a tuneup or the carburetor may need adjusting. Gas can drip or leak from damaged or missing gaskets, loose clamps or holes in the hoses or tank. When trash sticks between the needle valve and needle seat, fuel flows constantly through the carburetor to the crankcase.
Common causes for a lawn tractor to backfire through the carburetor include improper ignition timing or valve lash adjustment, worn intake valves or seats and a sheared flywheel key.
A loud pop called after-fire occurs when gas ignites in the exhaust system after the engine is turned off. You should let the engine slow to a complete idle before turning it off.
A bent crankshaft, a damaged crankshaft pulley or flywheel or loose bolts on the engine mounting can cause excessive vibration.