Lawnmower Trouble With High Carbon in the Spark Plugs

Spark Plug Function

• Combustion occurs when the fuel-air mixture delivered from the carburetor meets a heat source inside the compressed combustion chamber. The spark plug’s function is to provide the heat needed for combustion via an electrical discharge. Once combustion occurs, the heat force pushes the engine’s pistons, which then drive the crankshaft that holds the mowing blade. On average, The combustion cycle occurs 1,000 times per minute. So long as engine temperatures are at the optimal level per your spark plug's operation guidelines, carbon deposits will burn off.

Malfunctioning Ignition System

• The typical lawn mower ignition system includes the engine, a rectifier-regulator that determines how much voltage goes to the plug, and the magnetized flywheel. A weak ignition system in your lawn mower engine can reduce the voltage sent to the spark plug or send intermittent voltage. Check the regulator-rectifier to see if it is operable by testing for resistance. Magnets on the flywheel are sometimes attached by glue, so ensure all magnets are on. Also check connecting wires for obvious damage.

Fuel Air Mixture

• Most mowers come with a choke control system that allows you to increase the amount of fuel for the ignitable vapors. A richer fuel-air mixture helps start a cold engine. If the choke control is left on or the fuel mix is too rich, the engine may be flooded and the spark plug will continuously fire without igniting anything. This causes carbon fouling since the temperature never raised high enough for self-cleaning.

Low RPM

• Keeping your mower’s engine at idle produces low RPMs. This causes low heat in the engine because, at idle, not as much gas is introduced for combustion. This is not conducive to spark plugs because they require high temperatures to burn off carbon. Check your fuel delivery system for clogs or malfunctioning parts like the fuel pump to ensure your mower is able to reach high RPMs.