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1996 challenger 787 4200 rpm problem

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#1
Hello there,
2 stroke single engine 1996 787 challenger does not exceed 4200 rpm, doing 10 miles sped in the water, please help engine renewed, turbine renewed, carburetor renewed, I suspect the rotary valve is possible?
 


mikidymac

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#2
Sounds like the RAVE valves might be sticking closed.
 

JeremyD615

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#4
I open up the valves of the engine is still the same,

valves open when engine starts
I’m not sure what you mean by this... The RAVE valves are pressure actuated in the exhaust, so there is no manual opening of them. If the springs are removed from them or the caps are taken off, the motor will have a hard time getting past that rev range as well.

Another possibility is the rectifier. They can cause problems in that rpm range when they go bad as well.
 
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#5
I checked the valves on the engine, I didn't check the only one in the exhaust, I'll look at it thanks
 

JeremyD615

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#7
There are only two rave valves, and they are both on the engine. The similar looking valve back on the exhaust is the water control valve. That shouldn’t be messed with at all if it’s not leaking or giving you trouble.

The rectifier is what regulates voltage between the stator side of the charging system (AC) and the rest of the electronics (DC). You can test it by disconnecting a red wire on the unit itself, but I’m not familiar enough with the electrical box on the challenger to give you detailed instructions on how to do that...
 

jts32

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#8
The rectifier is in the gray electrical box in the engine compartment. It is underneath the starter solenoid. It will have 3 yellow wires and one red wire coming out of it
 

Ckrawiec

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#9
what is the rectifier.
As jts32 has stated where the rectifier is and what it looks like....there are 3 yellow wires and 1 red wire as part of the rectifier. The yellow wires take AC voltage generated by the stator inside the engine and the rectifier converts that to AC voltage for the ski's electrical needs and to also keep the battery maintained above 12.5/12.6 for the next start cycle of the machine.

To test your stator.....remove the 3 yellow connections to the rectifier and hold them in your hand, using a voltmeter set to the OHMs scale, test the wires 1-2, 1-3, 2-3.....you should get roughly .5/.6 between the pairs (all equal or pretty close - I got .6, .6, .5 (close enough)). Reconnecting the yellows doesn't matter just match the connections (male to female). This will tell you if your stator is OK. Machine is NOT running for this test btw.

A running machine with a good rectifier will put out roughly 13.5 to 14.5 V AC out of the rectifier onto the RED wire. That RED wire then feeds the ski the DC voltage it needs and keeps the voltage on the wire back to the battery side of the solenoid post. A simple way to test is the rectifier is working properly is to meter the voltage at the battery with the ski running...you should see 13.5 to 14.5 at the battery....if its bouncing all over the place...suspect bad rectifier....if you see 12.5 therabouts steady (good battery voltage).....the rectifier could be faulty OR you don't have continuity on the wires through the ski from the rectifier back to the battery (so test all wiring through the ski for corrosion, etc...)
 
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#11
As jts32 has stated where the rectifier is and what it looks like....there are 3 yellow wires and 1 red wire as part of the rectifier. The yellow wires take AC voltage generated by the stator inside the engine and the rectifier converts that to DC voltage for the ski's electrical needs and to also keep the battery maintained above 12.5/12.6 for the next start cycle of the machine.

To test your stator.....remove the 3 yellow connections to the rectifier and hold them in your hand, using a voltmeter set to the OHMs scale, test the wires 1-2, 1-3, 2-3.....you should get roughly .5/.6 between the pairs (all equal or pretty close - I got .6, .6, .5 (close enough)). Reconnecting the yellows doesn't matter just match the connections (male to female). This will tell you if your stator is OK. Machine is NOT running for this test btw.

A running machine with a good rectifier will put out roughly 13.5 to 14.5 V DC out of the rectifier onto the RED wire. That RED wire then feeds the ski the DC voltage it needs and keeps the voltage on the wire back to the battery side of the solenoid post. A simple way to test is the rectifier is working properly is to meter the voltage at the battery with the ski running...you should see 13.5 to 14.5 at the battery....if its bouncing all over the place...suspect bad rectifier....if you see 12.5 therabouts steady (good battery voltage).....the rectifier could be faulty OR you don't have continuity on the wires through the ski from the rectifier back to the battery (so test all wiring through the ski for corrosion, etc...)
Fixed the AC/DC mix up.

Are you sure about the units (ohms, or megohms) on your resistance values?
 

jts32

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#12
Thank you for your interest attached to my mpem
The two large red wires are going to your starter solenoid. Underneath the solenoid you will find the rectifier. Unplug the red wire from the solenoid and see if your rpm's improve.

With the red wire unplugged, your battery will not be charging, so don't run for an extended period of time.
 
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#13
The two large red wires are going to your starter solenoid. Underneath the solenoid you will find the rectifier. Unplug the red wire from the solenoid and see if your rpm's improve.

With the red wire unplugged, your battery will not be charging, so don't run for an extended period of time.
thanks, i'll try it today
 

jts32

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#15
With the boat on the trailer and shift lever in gear, are you able to rev to full rpm? If yes, your limiter is not the problem, as the boat doesn't know if it's in the water or not.

If you are hitting full rpm on the trailer, my guess would be your RAVE valves aren't opening under load. Had that issue with a couple of skis. New RAVE valves and bellows and all good
 
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#16
With the boat on the trailer and shift lever in gear, are you able to rev to full rpm? If yes, your limiter is not the problem, as the boat doesn't know if it's in the water or not.

If you are hitting full rpm on the trailer, my guess would be your RAVE valves aren't opening under load. Had that issue with a couple of skis. New RAVE valves and bellows and all good
I tried the full throttle while the boat was in gear in water and trailer.
The result is the same maximum 4200 rpm.
rave valves stand well boat pushes valves up while sliding.
should I squeeze or open these valves fully.
thank you very much for your help.
 

*_*

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1996 Sea-Doo Challenger
#17
Hey guys, similar problem with my 96 Challenger that I just started a thread with, but when I first get the boat in the water it runs great, but after going to idle I have the same issue. Boat revs to max out of water.

This started after cleaning the rave valves. I don't have the rebuild kits in yet so was just a clean and reassemble. Any thoughts? I hope the rebuild kits will magically make my boat work again.
 

JeremyD615

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#18
This is just a thought, and I don’t have enough of a sample size to say this with certainty, but I think cleaning the raves may be contributing to the problem. The gas seal is made by the tolerance between the valve stem and the aluminum housing, and as they wear that gap grows larger. I’m thinking some of that carbon build up that was on the stem was making up for a loose tolerance, and when you cleaned them, it opened it up.

If this is the case, the fix would be new housings and/or rave valves. Unfortunately that’s not a cheap thing to experiment with... Do either of you guys have another ski with the 787 motor that you could swap housings with?
 

*_*

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#19
I don't have another one to try that but it seems like a good idea. I was worried about that so left the stem alone, which could also be a cause I guess.
 

JeremyD615

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#20
I had some issues in my 96XP with some missing rpm up top. I got some of it back by replacing the housings, but the biggest difference on mine was going back to the softer stock bellows. They new replacements were stiffer, and I just don’t think it was building enough pressure with the larger tolerance between the stem and even the new housing.
 

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