My V6/280 started running roughly a couple of weekends ago while accelerating slowly from a stop. It seemed like it was vibrating for short bit while coming up on plane and then smoothed out. The boat was out of the water last week for a power steering pump repair (which was done) and I mentioned it to the dealer, but I guess they didn't look into it. When I took the boat out Friday evening, I noticed the roughness was getting worse and is noticeable in neutral beyond 2,000 RPM.
My initial theory was water in the gas as the tank had dropped to 1/8, but I added some ISO Methyl Hydrate (safe for FI engines) and put 40L of fresh fuel in the tank and went for a ride, with no improvement.
The boat will come out of the water for the season after this coming weekend and will go back to the dealer, but I was just wondering whether anyone has had a similar problem and what it might be.
I was thinking, fuel, fouled plug, plugged injector or something ignition (computer?) related. It ran smoothly from new, until recently (with 23 hours now).
Thoughts?
PS What a short season here: June 15th - September (kids have lots of activities on the weekends starting mid-Sept.


