The most common reason for a spark plug to foul is because the fuel mixture is too rich. This means that there is too much fuel and not enough air in the mixture. This can cause the spark to be weak or even to not spark at all, which will cause the engine to stall.
Choke is stuck open
If the choke is stuck open, it will allow too much fuel to enter the engine, causing the mixture to be too rich and foul the spark plug.
Faulty fuel injector
A faulty fuel injector can cause too much fuel to be sprayed into the engine, which will also cause the mixture to be too rich and foul the spark plug.
Worn piston rings
Worn piston rings can allow oil to enter the combustion chamber, which will also cause the mixture to be too rich and foul the spark plug.
Air filter is dirty
A dirty air filter can restrict the flow of air to the engine, which will cause the mixture to be too rich and foul the spark plug.
Spark plug is the wrong type or is damaged
If the spark plug is the wrong type or is damaged, it may not be able to provide the correct spark for the engine, which will cause the mixture to be too rich and foul the spark plug.
Faulty ignition coil
A faulty ignition coil can cause the spark to be weak or to not spark at all, which will cause the engine to stall.
If you are experiencing problems with your 2007 Honda 420 rancher ATV spark plug fouling, it is important to identify and correct the cause of the problem as soon as possible to prevent further damage to your ATV.
