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Loss of horsepower on last trip


Community Supporter
Jan 19, 2012
Miami, FL
Mako 21LTS Bayboat
I think i solved the problem but am always welcome for feedback (Kipp lol)... I noticed the spark plug coil that connects to the spark plug had a small cut on the rubber part. My buddy who's a boat mechanic said it was minimal and wrapped it with some kind of paste and electrical tape and said it should be fine... When i took my boat out last weekend, it topped off at 5000 rpm when it normally goes up to 5600-5700 rpm. Felt like it was running on 2 cylinders instead of 3 with loss of horsepower. I was gonna replace the spark plugs and spark plug coil ($97 for the coil) but he told me to start with just replacing the spark plug since it looked like it was going bad and he has seen spark plug connectors look a lot worse than mine looked and still worked fine.

To make a long story short, I replaced all 3 spark plugs and the motor cranked fine. Also bought Sea Foam in case theres deposits in the carb causing the motor to run sluggish... I'm hoping it was just a bad spark plug but I know i will eventually have to replace that coil. I won't be able to tell until i run her wide open again.

Any suggestions based on my issue? If you have any other options rather than the route i went, let me know. I'm trouble shooting with the spark plugs 1st, coil, 2nd then thinking it may be the carb if the 1st 2 options don't give me the horsepower back.