www.iFourWinns.com

Yea.. makes sense. Bill I can almost guarantee you'll see a big difference with new filters. How about your plugs. The ethanol in the fuel really promotes microbial contamination over time. I'm working on large fuels projects for the DOD and it's amazing what we are seeing in the mogas ASTs.

Plugs were replaced last season, and now probably have about 20 hours on them. I can pull some to see if there's any issues.

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-Bill Kearney, 2005 348 Vista

My vote is drag. New our 328 topped out at 5100 RPM, 42 MPH, last year with 6 year old bottom paint but no growth, the best it would do was 37 at 4600 RPM. Even though the boat only had 200 hrs, I thought the engines had dropped power over time. Just had the bottom painted and it runs like new, same speeds, same as new RPMs. Last year I checked the bottom and really thought the bottom was pretty clean but apparently not.

Eventhough you've lost more RPM's, it could still be drag since my experience is that inboards may be affected more by drag since the props slip less than IO's. At 4000 RPM is the boat getting the same cruise speeds as it did a couple of years ago? If yes then I'd start looking at fuel, plugs, ignition, etc. Let us know what you find

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2014 Vista V435
2011 Glastron GT180
2013 Sea Doo RXT-260

Bill did you ever get this fixed?

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2008 V358 Two-tone Blue V/P Dual Prop 320 HP
Lake Winnipesaukee, NH