96 GTI 717 Tuning

[skrillac]

Just finished a top end rebuild of my 717 and replaced rotary valve and cover. I also completely rebuilt the fuel and oil system, including replacing grey fuel lines with mpi grade fuel injection (black lines), all filters inline, rebuilt carbs with osd return to oem kit, and rebuilt the fuel baffle that had a falied float. I've verified each carb has 40-42psi pop off pressure. I've taken it out on the lake and successfully broken it in after a few hours of various throttle positions. The first few times I went out I was very conservative using the throttle. Only ever went to 1/2 throttle. Went out with the tach each time to watch rpms during operation and after releasing throttle to check return to idle. I never really noticed anything too big a deal, sometimes the idle would return to 1400-1450rpm range, usually 1500-1550rpm. Yesterday I took it out to really test the high speed and takeoff operation. At first I didn't notice any issues, but then i remember a long straight away where i looked down to check my tach at full throttle. I was only getting to 6450, maybe 6500 rpm max. I remember reading somewhere that the rev limiter in the mpem limits around 7200 rpm i believe. I assumed possibly i'm not getting enough fuel at WOT. Maybe an hour later, on my way back into the dock, I noticed that higher than 1/2 throttle was loading up the engine (bog). After getting the ski back on the trailer I remembered that low throttle (from 0 to 1/4 throttle) had always (since my rebuild) bogged a tiny bit, but I previously didn't think anything of it because response past it was solid, until my testing of WOT.

I pulled spark plugs (new, less than 5 hrs) to check coloration. I'm seeing a chocolate color on the bit that reaches into the combustion chamber. I also verified my compression is right at where it was right after i rebuilt it (before the engine had seen any water time). I have been starting the ski by opening the throttle a little bit instead of using the choke. At this point I have about a half tank of gas.

I have high speed screws turned all the way in (from what i've read it acts more like a bypass). My low speed screws are set a quarter turn cclockwise (slightly rich) from spec of 1.25 turns out from closed (1.5 turns out).

1. Is my observation of return to idle rpms (sometimes in the 1400 rpm range, sometimes in the 1500 rpm range) normal?
2. Am I correct in assuming that my engine is starved for fuel at high rpm (WOT)? should i open up the high speed screws 1/4 turn from closed?
3. Is my pop off pressure too low to receive proper fuel delivery when gas level is low?
4. Does it sound like my low speed screws are set wrong?

 

[mikidymac]

Set the screws to spec and the idle to spec.

When you say all inline filters, you only have the oem strainer correct?

Also did you replace the fuel selector?

 

[skrillac]

@mikidymac

The screen in the fuel baffle tube wasn't replaced as it was fine. The inline filter pn #275500089 (# 16) was replaced. Filters in the carbs were replaced too in the osd return to oem kit. I'll turn the low speed screw back to where it should be at 1.25 turns out from closed and see if my issues go away

Fuel selector was also replaced.

 

[mikidymac]

If you only replaced the fuel strainer element #16 and not the square cut o-ring #17 that could be the issue.

Those o-rings are notorious for leaking and causing fuel starvation.

 

[skrillac]

If you only replaced the fuel strainer element #16 and not the square cut o-ring #17 that could be the issue.

Those o-rings are notorious for leaking and causing fuel starvation.

@mikidymac

I really don't think that oring is leaking. If it was wouldn't the bowl be empty?



Anyways. I found that the pto side carb actually had its low speed screw turned out 1.5 turns, while the mag side was turned out 1.25 turns. Manual calls for 1.25. I think I may have tried to match the carbs, when in reality the threads on those screw holes may be completely different. I've turned both out to 1.25 turns now and will put the airbox back on and test.

 

[AlexD]

I also have a 2001 GTI 717 that I am experiencing similar issues with. I recently bought it and replaced fuel lines after fuel strainer and rebuilt carb with Mikuni kit. I ran it and it seemed to run good for first 30 minutes and then also started bogging after 1/2 throttle on the way back in. As I got closer it seemed to bog more all throughout the throttle range. And eventually I could only idle without the ski shutting off. When I got home I found milky oil on the plugs and also realized that the exhaust manifold has a leak letting water into the body and hopefully the root of my milky plugs. Can't imagine it would be the cause of our bogging tho. Curious to see anything you might find with yours.

 

[skrillac]

I also have a 2001 GTI 717 that I am experiencing similar issues with. I recently bought it and replaced fuel lines after fuel strainer and rebuilt carb with Mikuni kit. I ran it and it seemed to run good for first 30 minutes and then also started bogging after 1/2 throttle on the way back in. As I got closer it seemed to bog more all throughout the throttle range. And eventually I could only idle without the ski shutting off. When I got home I found milky oil on the plugs and also realized that the exhaust manifold has a leak letting water into the body and hopefully the root of my milky plugs. Can't imagine it would be the cause of our bogging tho. Curious to see anything you might find with yours.

I am technically missing one of the allen bolts that holds the arrestor screen retainer (piece of metal, not the flat piece). I can't imagine that would affect me, as I'm not seeing water get into the engine.

 

[1of500]

@mikidymac

I really don't think that oring is leaking. If it was wouldn't the bowl be empty?

View attachment 58329

Anyways. I found that the pto side carb actually had its low speed screw turned out 1.5 turns, while the mag side was turned out 1.25 turns. Manual calls for 1.25. I think I may have tried to match the carbs, when in reality the threads on those screw holes may be completely different. I've turned both out to 1.25 turns now and will put the airbox back on and test.

When it leaks it allows air into the fuel honestly I replace that oring every time I take that apart

 

[mikidymac]

Any airleak in the system even small can starve the engine of fuel. If it runs fine then starts to go south try opening the fuel cap and see if that helps, you could have a bad vent check valve.

 

[skrillac]

I did replace #275500087 (# 39) when i was rebuilding the fuel system. I kept #275500104 (# 21) in place because it seemed to function. I'll go ahead and replace #21 and #17, and check #39 again.

@mikidymac

are you talking about #37 or #38?

 

[mikidymac]

#39 lets air into the tank to prevent a vacuum and #21 lets pressure out at about 3-4 psi to stop overpressure.

 

[skrillac]

#39 lets air into the tank to prevent a vacuum and #21 lets pressure out at about 3-4 psi to stop overpressure.

I brought it back out to the water to test the new low speed screw position. I need to bring the idle up a tad. Was able to bring ski to WOT again at 6300-6400 rpms. Wouldn't go further. Wasn't hesitating wasn't loading up. Just wouldn't go faster.

Maybe 20 min later I started noticing bogging after 1/2 throttle. Made it a bit difficult to get back to the dock. I did notice slight popping coming out of the exhaust at this time, more than normal. Tried taking gas cap off and throttling high in neutral (so waves wouldn't go inside tank). Tach showed the same result, bogging at 3500 rpm.

I also filled the gas tank back up, thinking that would help. No change.

I think it may be less likely to occur when the engine is somewhat cold. I'm gonna replace #21, #17. I'm not sure what else could cause this.

 

[skrillac]

Went to go test the regulator/rectifier today, thinking that might be the issue. Hooked the ski up to the hose and noticed this guy.

@mikidymac Should I just take some of the jb weld steelstik and slap over that hole?

Now that I think about it, I did notice a higher amount of water in the hull than normal the last few times I've been running the ski.

@AlexD i think our issues are related.

 

[mikidymac]

That very much could be an issue. The easy fix is to sand the area with something really rough like 80 grit then use the steel stick epoxy.

A new welded plug would be the best long-term solution.

 

[Poormanracing]

Pull the mag cover and clean the connector I am pretty sure you have water in the housing from being power washed buy the exhaust plug.jb weld works but welding it is best.

 

[skrillac]

Well, I'm pretty sure the water leak was causing the bog. I had a friend take the ski out for an hour or so. He didn't notice any issues accelerating. I took it out again today for a bit and tested it all throughout the throttle range. I ended up using steel stik around the plug in the exhaust and using a bore camera to help with placement and coverage. @AlexD thanks again for the tip.

I also brought the idle up on the ski a bit so I'm not falling below 1400rpm like I was.

I am noticing that i still top out speed at maybe 3/4 throttle. speed-o shows 50-55, but i know those are off a bit.

@mikidymac
I'm wondering if i open the high speed screws from closed to maybe 1/8-1/4 turns out this will go away.

 

[mikidymac]

The 720 GTI will top out at about 45-50 mph and the speed doesn't change much from 3/4 throttle on up. They are a small engine in a big hull so yours sounds normal.

 

[skrillac]

Good to know. Thanks for the help guys. Time to work on cosmetic parts

 

[Mekanix]

I have some questions for you.


-Whats the compression now that you've run it a bit. 150-155?
-Have you done a plug chop at full throttle? Tan color on both? Lean, rich?
-Do you have an impeller or pump from an 800 model gtx, gsx in there?
I have used those impellers and it drops the rpm to exactly what your describing and I've seen this on a few other machines I've encountered.

That gusher comming put of the Welch plugs was likely going straight into the intake so I'm sure that wasn't helping lol

When you rebuilt the top end what base gasket did you use? How many small holes were stamped in it, 5 ? They like a 3 hole gasket better,
Did you check the squish after you were all done ? Aim for 1.3-1.5mm. Or 40-55 thou. 5 hole gasket gives usually 1.9-2.3mm squish


FYI stuff:
The low speed tapers off around 4300 and the mains start to really contribute around 4500-4800. You can feel the little flap on the half moons open up. With new kits in there they are stiffer and don't open as easy so you end up with a lean condition just around 4500, it can either trail off and drop rpm or jump to the mains. If you feel this, thats why.
The low speed screw is only for idle. It doesn't do much after that so If your getting bogging or hesitation there, look at lowering pop off slightly or going with the next size pilot jet. Or clean the carbs low speed again. I usually close the low speed screw, remove the pilot jet and use carb cleaner straw inside a piece of 1/8 oil line and spray half a can through there. Makes quite a difference. All the flow and force goes through the low speed holes, it doesnt take much at all to restrict flow here.

Replace your fuel in and return line with a clear and watch for air bubbles. That will tell you for sure if you have a selector or filter/water separator issue.
You can run it but will loose top end like you are if there are air bubbles in the lines. I had one filter cup that was cranked on so tight that it deformed and never sealed right unless it was cranked on that tight again. Clear lines were my only telltale.