1993 Nautique Speed issues

I have just bought my first nautique last summer and have noticed some issues with the speed. It runs max speed of about 35.5 mph and around 3600-3800 RPM. What is wrong.

By the way I asked this on another forum and was told to come over here and ask.

Thanks in Advance

Glad you decided to pop your head in here... I think you'll get much better advice from this group.

Your speed vs. rpm numbers, if accurate, lead me to believe that your propped appropriately for the transmission. You most likely have a 1.23:1 and somewhere around a 14x16 prop... though a 1:1 and 13x13 would be the other possible, but less common, option. Do confirm the engine ID (metal tag on intake manifold), the transmission (plate on transmission) and prop make/size (stamped on the prop, most likely on the hub face) if you can, though.

You most likely have an engine tuning issue, though. The first thing I do on a new-to-me boat is to tune it up and eliminate as many unknowns as possible. God knows the last time the engine has been gone through. That means plugs, possibly wires, cap/rotor/points/condensor, if applicable, set dwell (if points) and check the timing. If you have the Protec ignition (common in '93), much of that does not apply. Replace the fuel filter/water separator as well.

Once that is done, I would look at the carb more closely. Your issue is occurring right around where the secondaries should be kicking in... so I would be checking that next.

It has new plug, cap, and rotor. The holley power valve was replaced at the end of the summer last year with a new gasket kit. The weird thing is that the engine doesn't sound like it is running bad or rough. It is like it runs out of throttle cable. It runs fine and smooth at its current top speed but wont run any faster.

THanks for the heads up about this place.

A real simple first check would be to make sure the cable is fully engaging the throttle on the carb. Do you recall hearing the secondaries kick in?

Upon further checking, the secondaries are NOT engaging. The piece on the throttle body that the idle set screw adjusts will not allow the throttle to go far enough back to engage the secondaries.

Now what?

Gary S wrote: Cannot check it that way Jason.The easist way is to get a driver, have the motor box open and run it up as you go,then push up on the pushrod that comes out the bottom of that round cover,that way you are manually opening the secondaries. The diaphram you need to check is under the round cover with the 4 screws at the top of this picture-

I am not arguing with you, just a very curious and inquisitive person.

Why can't I check it that way? When the throttle is full open(by both the shifter and on the trottle body) the push rod from the main throttle plate(plate where the throttle cable is attached) to the secondary plate(plate on the same side as the main throttle plate) will not move back far enough to engage the secondaries.

I put the text in parenthesis in case I was calling it the wrong thing.

Thanks
Jason Skelton

I suppose you can then,you didn't say you opened the throttle.I know with the carb just sitting there with the throttle cable disconnected you can't. The carb does not have mechanical secondaries,if it does it's not a marine carb for your boat.Anyway vaccume opens it not any linkage.So it is possible that your diaphram is bad.Try it like I said above, when you open them by hand and if their not stuck you'll know it

Gary S wrote: I suppose you can then,you didn't say you opened the throttle.I know with the carb just sitting there with the throttle cable disconnected you can't. The carb does not have mechanical secondaries,if it does it's not a marine carb for your boat.Anyway vaccume opens it not any linkage.So it is possible that your diaphram is bad.Try it like I said above, when you open them by hand and if their not stuck you'll know it

So the secondary plate beside and behind the main throttle plate is just to keep it from "overrunning"?

JasonS wrote: I finally checked it and the secondary plates are not sticking. They will open up when I push the rod under the secondary diaphragm.

Thats good,their not stuck. Now you could water test it like I said above and see if you pick up rpm's.If it does then you could try just changing the diaphram or better yet time for a carb rebuild