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I have noticed that my motor a few times drops RPM down from 5200/5500 to 4000 and the boat slows considerably when I am at WOT. It doesn't do it all of the time. I can then bring boat to neutral and then open it up again and it goes back to 5200-5500 rpms. I know when I over trim and hit rev limiter I lose all power. The boat is a 22 foot Fisher on 25 inch pontoons with 4 people and a full tank of gas. I run a SS 13p 13 3/4D Solas Rebex NS3 prop. Recent changes was I raised my motor up one notch which did increase my RPMs and speed a bit. Could I be grabbing air and need to go down a notch? WOT RPM for the boat is 5000-5500. When I first raised it i went to 5800-6000 RPM but the second time I took it out it seemed to settle around 5200-5500. Trimming the motor doesn't affect the RPMs at all nor engine sound that I can tell.
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Long time ago I was a fisher/mercury boat dealer. Did not sell a lot of pontoons, salt water dealer.
You didn't say anything about acceleration or rough running so it sounds like fuel starvation.
I would change on motor fuel filters and test drive on a separate 6 gal fuel tank and fuel line. -
Thanks Massbay.... The engine purrs like a kitten and seems to accelerate well. I pulled the spark plugs and they were black with carbon but not too bad. They have 2 summers on them. I have checked air filter and I looked to see if there was water to drain from below fuel filter. Nothing came out. Fuel filter looked clean but I am going to change it out and try the separate tank and fuel line. It doesn't seem that its a rev limiter issue too me. If it was rev limiter wouldn't i lose complete power. I am finally at max RPM with this motor height.
Motor is a 2010 Mercury 115 Optimax DFI sitting on a 22 foot 2003 Fisher pontoon with 25 inch pontoons. I am at the upper limit of RPM and so i might play around with an increase to a 14P prop.Comment
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If you hit the rev limit you'll know it. motor really skips very badly.
merc had an issue with the grey fuel lines going from tank to motor, causing a fuel flow issue.Comment
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Drain hole was clogged in VST tank. Water separator was about 1/3 full. I unclogged the drain and drained it. Replacing hose and primer bulb Friday. Hope to take it our Saturday and see if it makes a difference.Comment
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Did changing the primer bulb end up helping?
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Happy Boating!
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