96XP, idles fine, runs GREAT, but bogs on acceleration

[scooper77515]

Idles fine, bogs and dies when you try to accelerate. If I can get it past 25% throttle, it will take off and run great all day, as long as I don't let it go back below 25% throttle.

Works best if i start it with throttle already 30%, and keep it there.

Rave issue or carb rebuild time?

 

[seadoosnipe]

Quick Reply!

Sounds like your rave valves are sticking open. These are very simple to pull and clean. There suppose to be done annually. If it's been several years, then they probably have carbon deposits that are causing them to stick.

I'm going in to read a little on your application to make sure there's no more info to give you. I'm assuming you have the 787 Rotax.

If there was no gogo, then I'd go with carbs. But you say that it runs good top end, so it doesn't sound like carbs......clean the rave valves first, pay attention to their orientation and make sure you put them back on the same cylinder head they came off of. Check the rubber diaphragm for leaks and/or tears and holes. If your running the 787, then the little red caps that adjust spring tension should be flush with the edge of the black cap around it.

O.K...I just looked it up and yes, you do have the 787 Rotax, so follow the above steps. I'm pretty sure this will take care of your problem. Let me know what your results are!...I'd love to hear how it works out for ya!....

 

[scooper77515]

I will try that today and see what happens...

Thanks for the quick reply.

 

[seadoosnipe]

MAG side!

The rave on the MAG side is a bit hard to get out. But don't take off the exhaust system to do it!.....you can get a metric socket or wrench and seperate the valve from the diaphragm actuator with the black plastic looking nut under the cover. You won't have to worry about the valve falling through, it has a stopper on it. That will make it easier to remove than taking off part of your exhaust system. The PTO side will slide right out.

 

[scooper77515]

They came apart really easily. I still don't quite get how they work, but they were definitely gunked up pretty bad. I cleaned them both up really good, everything seemed to move freely, and put them back in.

Still didn't fix the problem.

What I did notice today when testing it out is that if I put the choke on about halfway and start it up, I can accelerate through the 20% range, then quickly kick off the choke and it will take off and run fine...

Still sounds like a carb rebuild time...need to do it anyway. Hope it fixes the bog.

Again, thanks for your help. Those RAVEs needed to be cleaned up anyway.

 

[seadoosnipe]

Carbs!

When you listed the year of your doo, I wondered how long it had been since they were last cleaned. They are part of your exhaust system. When your at idle, their at the lowest position to maintain combustion pressure, as you speed up, the pressure increases causing the valves to open. The more fuel and air you can exhaust, the faster you can go.......That's about the best way to describe it without writing a book on the theory of the RAVE (Rotax Adjustable Variable Exhaust) system.

It sounds like your carbs are ready for a rebuild too. Since your rave valves are clean and when you tested it, you were able to pull your choke to get a better response, then your fuel pressure should be checked and your pilot valve. If you take off your air cover and spark arrester, you notice two small fuel lines coming from a diaphragm from your PTO side carb (where it's located in the sport boats, may be located on a different area of the carbs in a PWC) leading to your carbs, it will split off with a "T" going to each carb. If you look into the carb while rolling the cam wheel on your throttle, you should see and if it's quiet enough, hear fuel being squirted into your carbs. This is the fuel needed to increase rpm's as your throttle plate opens. Once your throttle plate passes a certain point, then the main jet (which from what you describe seem to be jetting fuel fine) kicks in and the ski takes off.....
I hope this helps a little. Some of the other moderators and the administrators ride PWC's.....if I've missed something, they'll let you know what else you may want to check for!
Hope your ridin hard again soon!

 

[scooper77515]

Oh, I am riding hard now...Just cannot ride soft...that is my problem

I put in 2 hours on the water today going almost full on the entire time. Did an hour after cleaning the RAVEs and then another hour after adjusting the carbs.

Still doesn't take off well, but a little better.

I will get 2 carb rebuild kits tomorrow and clean and check the entire fuel system while i have them apart and out of the way.

Again, thanks for the help and suggestions. I doubt any of this has ever been done to the ski and it really needs it all

 

[seadoosnipe]

Carb cleaning!

I agree, if the ski is as old as it is and they haven't yet been rebuilt, then I agree, it's time to check them and replace gaskets and the like. Let me know how things come out. I'll be waiting patiently to hear of your progress. BTW, you'll notice on the PTO carb, there is a cable going to your oil injection pump. You'll need to make be careful not to change the setting on that cable or after you do a rebuild, make sure the pump is in sync with your carbs.........Good Luck!..

 

[scooper77515]

Thanks for the heads up. I will get two mikuni rebuild kits and hopefully have them installed by sunday or monday night and let you know how it runs.

 

[seadoosnipe]

Adjustments?

These carbs are classified into two carbs. The PTO carb and the MAG carb. Mostly by the way the linkage is set up. Make sure you set the syncro from the idle stop screw on the MAG and then syncro the PTO to it. Then you'll need to check your cable adjustment on your oil injection pump.
You might drop Joe a line, because he's pretty much set on doing away with the injection pump and going premix. For a ski that old, he may recommend it so that you don't have major problems down the road. Personally, I still use mine, but I am constantly working on it too. I think I work on my 787 more than I take it out to play. It's like a tinker toy!.....LOL....

 

[scooper77515]

Interesting idea on pre-mixing...I have been...anxious...I guess that is a good word, on the injection pump. I can just imagine it going out 3 miles down river...

 

[Wheels & Waves]

Carb rebuild

The 96 XP does not have accelerator pumps on the carbs. There were some models (GTI and others) that had acc pumps. You definitely need to rebuild the carbs. I'll bet the fuel screens are pretty well clogged up. You also need to set the correct pop-off pressure on each carb. It should be set around 25psi to 40psi and the needles are High @ 0 turns and Low @ 1 1/4 out.