95 Ski Nautique speed is bad but rpm's OK

[BadgerNautique]

I have a 1995 Ski Nautique with 525 hours. I replaced the spark plugs two years ago. I have done oil changes and winterized it every fall (live in Wisconsin).
Last year I had two big problems:
1. My oil pressure gauge stopped working. This may be the oil pressure sending unit so I am not too worried but will get this fixed.
2. After 35 mph the boat just doggs down. I can't come close to 48-50 mph like a few years ago. The RPM's seem to be there but it is just sounds like it is choking. I have tried a few differetn engine cleaners and fuel additives to no luck.

Help!?

[MattM]

RE: 95 Ski Nautique speed is bad but rpm

fuel filter possibly, also could be a bad distributor, or may need carb-work, if its right about the point in the throttle that all four barrells kick in.

[skinautique]

RE: 95 Ski Nautique speed is bad but rpm

Which engine is in the boat?

[83sn2001]

RE: 95 Ski Nautique speed is bad but rpm

sounds like it is starving for fuel. Check your filter (or just replace it) and also your fuel pressure. Is the engine fuel injected? If so that could be a sensor gone bad. Check your advance in your distributor. It could be stuck and not advancing properly. You will just have to narrow it down by elimination. Start with the easy stuff, Fuel filter,distributor advance and go from there. Good luck

[BadgerNautique]

Engine Specs

Thanks for the help so far.
More information:
1995 PCM engine
EFI
285 Horsepower

Any more suggestions would be greatly appreciated.

[nms1991]

RE: Engine Specs

Is it a GT-40 or is it the tbi engine? but the first things you need to do is find out what your fuel pressure at that speed is (Gt-40 35 to 45 psi tbi at 14 to 17 psi). Then you need to proceed from there and troubleshoot systematically,(i.e. check for proper fuel, ignition, and compression). But if you notice a high pitched wine coming from the fuel pumps then first change the fuel filter then look at the pumps.

[Mikeski]

Badger,

Check you specs again, I don't recall the engine option you describe. I may be wrong but I think they offerred the GT-40 (310hp), pro-boss 285hp (carbureted) and possibly the throttle body injected 310hp motor.

Does it look like this:

[BadgerNautique]

Yes, my specs were off the top of my head and probably wrong. My engine looks exactly like the one you show.
So what do you suggest?
Thanks!

[skinautique]

Re: RE: Engine Specs

Is it a GT-40 or is it the tbi engine? but the first things you need to do is find out what your fuel pressure at that speed is (Gt-40 35 to 45 psi tbi at 14 to 17 psi). Then you need to proceed from there and troubleshoot systematically,(i.e. check for proper fuel, ignition, and compression). But if you notice a high pitched wine coming from the fuel pumps then first change the fuel filter then look at the pumps.

Follow these instructions and go from there

[Mikeski]

RE: Re: RE: Engine Specs

You are looking for 35-45psi fuel pressure, that's a GT-40 310hp motor (one of the best boat engines ever made).