Could somebody explain to me why my kawasaki twin engines foul the plug on the left (when looked from the back) cylinder? I've noticed it on four FH and FX engines. The right plug would be clean, but the left plug would be coated with thick/hard carbon. In the past I attributed it to overfilling with oil because the left cylinder seats lower. However, I am not certain that is the case. The engines seem to run fine once the plugs are cleared with equal compression on both sides. I also suspect the head gasket failure but don't want to act prematurely.
