The Lawn Mower Smokes & Will Not Start

Fouled Spark Plug

• The spark plug is responsible for igniting the fuel vapor, creating the hot gas that moves your lawn mower engine’s pistons. This combustion process occurs 1,000 times a minute, which can wear out a spark plug. If your spark plug is old and covered in debris, it can “foul” out and not light the vapors consistently, thus inhibiting the starting process. A fouled out spark plug combined with contaminated fuel can also create smoke.

Gas and Oil

• Lawn mower engines need oil to keep the working parts lubricated. This reduces friction and keeps the engine cool at the same time. A pump or paddle disperses the oil and distributes it into the engine during operation. Although oil is kept in a separate compartment, a tilted lawn mower can spill oil into the combustion chamber. Too much oil can prevent a full start because the fuel vapors ignite with oil contaminants in the chamber, creating white smoke from the exhaust.

Clogged Filter

• Both the oil and engine have filters to help remove contaminants as they go through their cycles. If the air filter gets clogged, there may not be enough oxygen allowed into the carburetor for a full start. A clogged oil filter could allow contaminants to bypass into the engine during operation.

Broken Piston

• Lawn mower engines, like car engines, use pistons to continuously compress and release hot gas throughout the engine. The hot gas pushes through the crankshaft and spins your mower blade hundreds of revolutions per minute. The pistons have gaskets that prevent contaminants from entering the piston chamber as well as maintaining the proper pressure for combustion. If a gasket gets damaged or blows, the piston loses its compression power and will stop the mower.