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1996 Sea doo XP motor shakes but won’t rev up

cops13579o

cops13579o

Member
I have a 1996 sea doo xp that I bought and had it running good for a couple trips but recently it had developed a condition that makes it unusable. What happens is it will the up real good for about 3 seconds after a start up but then it suddenly stops and the motor just shakes and won’t rev up no matter what. The interesting part is if you shut the ski off and start it back up it will run good again for about 3 seconds. I’ve tried research but can’t find anything. Thanks for the help in advance. Engine is a Rotax 787.
 
I would start with a compression check. If that checks out, check the exhaust for leaks, it would have to be leaking pretty bad, but if your running it with the seat on and it’s leaking it could be starving the engine for air, if you can get it to rev up to 4500 rpm, check the volts at the battery while it’s at the 4500. Could also check that the exhaust hoses haven’t collapsed internally. If all checks out good, might be time to rebuild the carbs? When was the last time they were done? Have you owned this machine long? When was the last time it ran correctly?
 
I bought it in February this year so this is my first year of owning it. Compression is good. It doesn’t have a tachometer but it’s definitely not getting to 4,500 when it ain’t running right but when it is it gets to 7,000 ish no problem. I think it’s something with the exhaust. The water box rave valve was leaking pretty bad before but I got it fixed now and still have the problem. It ran good when I first got it but just started having problems after I cleaned the rave valves for the first time. Sounds like the exhaust get blocked when it stops running. I have videos but don’t know how to post them. Thanks for the reply!
 
I think you will need to make a you tube video, and then you can post that. Will it rev up to 4000 to 4500 rpm good?
 
It will rev up to 7,000 real good then it will just stop and hardly go above idle. It’s hard to explain. I’ll try and get a video sent your way.
 
I would do the compression test anyways. I’m sure it is still good and not an issue, positive actually but just nice to go through the steps to be sure. Definitely put a volt meter on the battery and see what volts your getting at idle and at 4000 rpm. Maybe a bad voltage regulator
 
Oh, and I re read your post again. This started happening after you cleaned the rave valves? If so, have a look at them again, make sure there are no holes in the bellows and that the springs are in correctly
 
I did check the RAVE Valves and they’re in good. I got the new designed one with the slots in them. But that didn’t solve my problem but every part of the RAVE valve is clean and in good shape now.
 
Well, same, check the volts, check the exhaust hose to see if it has collapsed, re check the rave bellows. If all that is good, maybe it’s fuel air related but I don’t think so, just make sure high and lows are at factory settings.
 
I’ve done some testing on it and when I hook the motor up to water via a hose no water comes out the pea hole in the back. When I have it on the water it does come out of that. Not sure if that means anything or not.
 
So the problem is related to the front cylinder. If you take that front cylinder plug off it runs smooth and doesn’t shake the motor but as soon as you plug it in the motor shakes. It has something to do with the spark of the front cylinder. Does anyone have any suggestions.
 
Just a couple ideas, definitely not a for sure thing but with the shaking your describing I’m wondering if maybe the connecting rod bearing has spun and it’s out of phase. Just an idea, so let’s see what other ideas people have. Also, can you shake the engine while it’s off? Maybe one of the bed plate bolts is out or loosened? That’s fairly common issue
 
If You have ignition problems, check first inside the "electrical box" placed at front right, check cables there and coils, measure resistance on coils both primary and secondary side, compare values to the other coil ( The manual said 9K-15K, and for primary side: 0.34-0.62 ohms for this test).
in mine I had a small cable ( low voltage side of coil) rubbing against a metal part inside the box

Check everything in here for corrosion or broken / damaged cable , also check corrosion on the very hidden fuse....

and ofcourse clean the sparkplug cap, and check for corrosion there, Check also plugs and compare color /soot on them...

I said according to the Video that this is definitely a engine just working on one cylinder due to ignition problems.

By the way i reqognized it was a 787 NOW, my explanation and Ohm values is for the 951 engine, but should be in same "size" in Principle

1754483964633.png
 
Seeing this is a 1996 XP this symptom is typically a bad voltage regulator.

Unplug the red wire from the voltage regulator in the front gray electrical box and see if it runs normally.
 
I unplugged that voltage regulator. It ran good but I still had some issues with the front cylinder but the motor never shook like before but if I would uplug the front spark plug it would still run but if I unplug the rear it would die. How long can I run it with the red wire unplugged?
 
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