i have a 88 carver santego with newer (1998) 4.3 ltr mercruisers. started getting backfire issue on port engine at throttle up and cruise. seems fine at slow idle below 2000 rpm. checked spark plugs and noticed number 2 plug had rust and what looked like salt deposits on it. boat is in salt water river. i had changed the plugs earlier in the year and noticed the same plug was fouled out, but boat ran fine up till now. im guessing intake manifold gasket if leaking onto that number 2 plug causing a misfire. any other ideas?
