1996 GTI 717 Acceleration Issue

[K Huf]

The issue I am having on acceleration at WOT is that the engine sounds like uh-uh-uh-uh-uh unless I cut back on the throttle.

I bought this 1996 GTI 717 last year November 2019 as a project ski. It had been sitting for at least 4 years. The main problem was a pin hole in the exhaust which I repaired with JB Weld. Also while it was sitting, mice got into it and chewed the wiring behind the gauges. Wiring and multi-gauge were replaced. It appears that the engine had been replaced at one point as it has a single carburetor and the double style choke cable was disconnected.

So here is what I have done so far. Over last winter I rebuilt the carburetor with a genuine Mikuni kit and new needle and seat. Replaced the fuel selector valve. Replaced all the grey fuel lines with black automotive fuel hose. Replaced fuel filter. Replace oil lines. Installed new carbon seal and boot. Installed new wear ring. Installed new spark plugs. Checked compression, 130 in both cylinders. Took it out in May and it ran great, clocked at 46 MPH with GPS. Used it several times over the summer without issues. Took it out several weeks ago and the acceleration problem occurred, could only get to 42 MPH on GPS. Figured it could be a fuel issue. After consulting the Forum I by-passed the fuel selector valve and filter by connecting the carb inlet hose directly to the fuel pickup at the tank, same issue. I pulled the carb off and dis-assembled for cleaning. There was some crud in the carb fuel filter. Cleaned with carb cleaner squirting it through the jets to make sure there was flow out of the 3 holes. Checked pop-off which was at 32 PSI. Checked main fuel filter and it was clean. Put everything back together, took out to the river today and had same issue. Installed a new set of spark plugs, same deal.

Where do I go from here?

 

[Mraw]

I would test the rectifier, to test rev the ski to 5500 ish rpm, voltage at the battery should be between 13.5 and 14.5. Or you could disconnect the red wire and go for a very short ride to see if the issue goes away

 

[K Huf]

I checked the voltage at the battery while revving the engine and got 14.01 volts. Do you think maybe the rectifier is just starting to go?

 

[K Huf]

I was going to try cutting back the plug wires but it appears that have already been cut to the point that they will be too short. I am going to try replacing the plug wires.

 

[Gritzlor]

Wonder if it is catching air and cavitating, causing the engine to hit the rev limiter.
I had a bent driveshaft causing similar issues, it shook the carbon seal enough to let air in. Straightened the shaft and problem gone.
Seems like you did all the right things around the pump but there could always be something, too little pressure on the seals, torn bellow or such. It's easy to miss a detail.

 

[K Huf]

I replaced the plug wires. Still have same issue.

 

[JeremyD615]

Like Mraw mentioned, try disconnecting the red wire at the rectifier. I’ve found that the voltage test on the trailer doesn’t always tell the whole story with rectifier issues, and this does sound like a likely culprit here...

 

[K Huf]

Thanks for the advice. Sadly the ski is going into storage this week. Got to wait for spring.

 

[K Huf]

So I was able to get back out on the water. Unplugged the red wire at the rectifier and still had the same issue. Replaced the rectifier, same deal so I put the original rectifier back in. I had 2 people suggest 2 different things. First guy said the high speed carb screw needs to be adjusted which sounds strange because it ran great after I rebulit the carb and set the low & high speed screw to the original setting. Second guy says it is the MPEM rev limiter circuit going bad.
Any thoughts?

 

[POPPS]

doesn't 130 seem low?,,The high speed screw has nothing to do with this unless the orifice is plugged,,,have you checked the front E plug?,,,male and female sides?,,,(use a mirror),,have you checked the pickup/trigger?,,Maybe you missed something in the carbs,,,since you said you found some "crud" in there.

 

[K Huf]

The E-plug? Are you referring to the connection to the magneto/stator?
And what is the pickup/trigger?

 

[POPPS]

The E plug, is the connector at the front of the engine,,sometime.s a pin can become corroded and play "tricks,",,,the pick up is the sensor in the front cover to fire the dignal to the cdi/coil.

 

[K Huf]

Ok thanks, I’ll check that.

 

[K Huf]

I cleaned both ends of the negative battery cable and reconnected using silicone grease. Also cleaned the four wire connector to the magneto. Still have same issue.

 

[POPPS]

Gritz may be onto something,,,it may be cavitating,,,check the wear ring and prop.

 

[K Huf]

I am getting the same stuttering on the trailer with a hose hookup. But I will check the wear ring and prop next chance I get.