Today I lost 3 mph and 300-400 rpms each motor. This happened between one ride and the next. All gauges read normal including trim, except for the speed and lost WOT RPM's. Motors sound perfect at all speeds, no stumble, no miss. Visually examined props, drives, hull, tabs, all perfect. Boat can be felt to bog slightly and then loosen up again. I can't figure it out. By the way my boat is a 1997 31 Sonic with 454 Mag carbs, 200 hours. Also every once in a while at WOT a twitch could be felt in the steering ( standard merc power steering, not external ) . It feels like the boat is dragging something. Any ideas???

I think I will check the fuel filters and the gas in them, but I don't really have any solid ideas. Someone on this board always has the answer to anything, hopefully someone can help me.

I'm experiencing the same thing. I've checked the fuel filter, seperator, next is the fuel pump. Beyond these..I'm open for suggestions too.

I would try the easy stuff first, fuel filter& pressure, maybe check the spark plugs, how are they coloring{rich, oil fouled, lean} todays gas can be a problem sometimes, take a gas sample in a glass jar, let it sit for a while, do you see any water or trash in it, let us know what you find, good luck. Mark

Since the problem is the same with both motors at the same time I would think it has to be fuel related. Bad fuel filters could also be part of the problem if both engines sucked up something out of the tank. Chang the filters and put in a bunch of dry gas and some premium fuel.

Sounds like something isn't reading in corelation with the back of the boat ie; drives and/or trim tabs check with straight edge in relation to bottom and indicators.....next would be something fuel or electrical related.....try that and get back to me......

Sean

Thanks guys, I'm heading out to the garage to mess with it now. Both engines down on power is confusing me, as they feed off seperate fuel tanks. But I of course fuel them at the same place at the same time. I'll post any results as soon as I have some.

Sean, I agree with your guess, the trim for drives and tabs I checked as soon as I got it out of the water last night, including trimming the drives to their top speed position. I couldn't find a fault. I have solid hub props, so its not a spun hub.

I have an idea bring it to World Class Marine in Jersey....they can diagnose it and you will still have your shirt left when you're done....they'll even buy you lunch......Sean

856 498-9606

Check spark plugs for corrosion. Is it more or less humid/hot than earlier in the season? What condition is distributor in?