"I have twin Mercruiser 454's on a 40' Cruisers, Inc. My port engine recently stalled after running for about 30 minutes (the last 20 minutes at about 3,700 RPM. It began running very rough and wouldn't maintain RPM's, then stalled. It restarted, but idled rough and would not maintain any RPMs, then finally stalled again. Engine temp was normal (175), and no oil loss. About 2 hours later I was able to restart it and use it to pull into my slip. We tested the engine after it was restarted, and it was smooth at several different RPM's up to 3,000 (under no stress). The same thing happened the next time we took it out, after running for 30 minutes. I suspect it might be electronic, because I have digital tach's and when I tried to restart it the RPM's on the tach would jump around from 200 to 3,000 or so. It is a '94 with 1,200 hours, electronic ignition and 4 bbl Webber carb.
Where should I start?"