'95 Ski GT-40 question

Hey gang!

Our new to us 95 Ski seems to be, for lack of better term, "chugging" at WOT.

The best way I can describe it is compared to a carbed motor not all 4 barrels opening up.

It's up around 42-43mph at 4600 rpm running a 654 ACME 12.5X15.

It's right there, but feels just a tiny tiny bit short of what it should be.

I'd assume the basics..plugs/wires (not sure when those were done last) but didn't know if you guys had any secrets on these GT's.    Fuel could also be to blame I suppose. Haven't run a fresh brand new tank all the way through yet this year.

what rpm's are you running when starts to chug ?

mdvalant wrote: Haven't run a fresh brand new tank all the way through yet this year.

Come back after you get a few gallons of fresh gas through it. Certainly wouldn't hurt to inspect the cap & rotor.

That early gt40 in that hull should pull a 654 to 5200 and at least 46mph. You're a good ways off those numbers, something's up.

I would change the fuel filter or filters if this boat is new to you and you don't have the history.   If you are going to run it and burn through a tank of fuel I like to add a quart of automatic Transmission fluid to the fuel tank. ATF has many cleaning and lubricating properties that help clean a fuel injection system. It keeps the injectors snapping the way they should. I only do this once per season.
You might wish to put a fuel pressure gauge on it when you run it and see how the pressure is holding up when your power falls off.

The 95 has a temp sender and an oil pressure sender that can put your engine into limp mode if they go off at the wrong time. My coolant sender started making my engine stumble when the raw water pump was not putting out enough water to keep the temp constant. I guess I should be appreciative since I was able to fix it with no damage done.
I run a Acme 224 Prop and RPM above 5,000 RPM and top speed of 48.

4800-5000 is optimal for best all around performance but 5200 won't hurt it.

When the GT40 is running good it is pretty impressive for a stock engine.

Hey Mark, you say you run a 224 prop. We run a 1442 on our Sport Nautique and the tranny knocks or dampener plate makes a little tick at idle with that thing. Does the 224 do that to you?

TRBenj wrote: The tick is caused by the damper being worn or the idle needs to be adjusted, even if it only shows up with a particular prop, it is not the true cause.

Interesting...Sporty only has about 140 hours on it!   Doesn't do that on any other prop was kind of my thinking..

Hollywood wrote: The bigger diameter of the 1442 combined with the high pitch could be just loading the drivetrain enough to cause the rattle.

This is what I've been told in the past, HW.   That 224 has even more pitch than the 1442 so that's why I asked about it.

Fl Inboards wrote: In the mid 90's we had some 3/8" fuel hose that the inner liner tended to collapse on the suction side of the fuel delivery system. If it has it's original fuel lines in it I would be prone to go completely through the fuel system from the pick up tube and anti siphon fitting forward, inspecting and changing out the original fuel supply and return hoses, and checking that the vent hose was clear as well as the vent. along with a quick tear down of both fuel pumps, especially the low pressure pump as gradew seems to accumulate in the screen in the top of the pump.

You're killin me Jody. hahahaha Thanks for that, I think   

On a side note Mark, Skidim is listing new for '15, PCM ECM's for all GT40 efi engines at $572.69

I too was wondering what everyone's thoughts were on the ATF idea.

I would rather see Marvel Mystery added to the gas than ATF. Both are very similar with being heavy on detergents but the Marvel is designed as a top cylinder lube. The ATF is more on the hydraulic oil side.

Fuel injector cleaner costs about the same as atf last I checked.