What will a fouled spark plug do to your engine?

What will a fouled spark plug do to your engine?
A fouled spark plug will make you lose horsepower if the plug is not producing a good spark. The other thing a fouled plug can do is if it is not firing right the fuel that gets into the cylinder dosent get burned all the way and it is then pushed out the exhaust valve and goes into the exhaust system. from there the fuel can get hung up in the catalic convertor and then burn in the convertor and then you will nedd to replace the convertorit also causes the unburnt gasoline to wash the oil off the cylinder wall and cause undue wear