I have had a simlar problem (Johnson 90), with the extra feature of "skipping" or stuttering at around 4200 rpms. I replaced the fuel line and pumped up the bulb to find fuel squirting from around the top of the fuel air separator. Two screws had loosened about three turns! Well, I tightened (also replaced plugs ,cables, and coils). I still have this problem. Boats are such an adventure.