Why Does the Lawnmower Have Fouled Spark Plugs?

Spark plugs get fouled through normal use.

Fouled spark plugs prevent a lawnmower from operating at peak performance. Eventually all spark plugs foul from normal use. Engine combustion will gradually deteriorate a spark plug and it will require replacement.

Gapping

All spark plugs have a gap between the top of the plug and the bar that goes across the top. The spark crosses the gap. If the gap is too large or too small, the lawnmower will not run properly. Check the owner's manual for the proper gap size and use a gap gauge to ensure the spacing is correct.

Types

Black deposits on the tip of the spark plug are caused by carbon deposits created through normal use. If the tip of the spark plug is missing and there is no evidence of corrosion, this is the result of detonation. When the tip of the spark plug is missing but only partially and there is evidence of whitish deposits or corrosion, this is called pre-ignition. Detonation and pre-ignition indicate the lawnmower is in need of repair.

Wet Plugs

Spark plugs can become wet with gas because of engine flooding. Wipe off the plugs and restart the engine to remedy the situation.

References

• Toro Online Manuals: Worn or Fouled Spark Plugs