I have a 2000 Nissan 50hp outboard motor . It's run ok but is getting to much fuel in cylinder 1 and 2 when I check the spark plugs they are fouled out in cylinder 1 and cylinder 2 . I have changed the spark plugs twice and I have changed all of the ignition coils and rebuilt the carbs. Also bought a new gas line and tank. I can not figure out what's wrong with it . Please help!