NO torque but high RPMs

[hotrod6927]

I have a 1997 Challenger 1800. Last weekend I brought it out tot he lake and the left engine seems to be running fine, however, when I give it throttle it is good to about 4000 rpms and then it shoots up to 6500-7000 rpms and then fluctuates back and forth from 4500 and 6000 rpms. It does allt his with out me changing the amount of throttle I am giving it.

Also while I am doing this the boat will not get on plane and it seems like it is not producing any usable power.

I am not sure what the cause of this could be. I have read some threads that indicate that imay be the RAVE. And I also have read that it might be a cavitation issue.

When the RAVE is properly functioing should water"leak" out from around the black cap? Because the effected engine's RAVE does not have any water "leaking" from it and the engine that is functioning does have water leaking from it when it it throttled up. Is this how it should work? Is there a way to test if your RAVE is working propperly?

Any advise is greatly apreciated. Also I am not very familiar with boat terminology so please spell it out.

Thanks in advance

 

[kustomkarl]

You might consider doing teh annual RAVE valve cleaning. Here is some information on the RAVE valve, that might help you out;


RAVE VALVE annual cleaning

________________________________________The RAVE, (Rotax Adjustable Variable Exhaust) valves are located above the exhaust valve. There are 2 of them per engine. They are round with a red adjustment screw in the middle. It has a clip that holds it together. How they work is that they open the exhaust port larger as the engine rpm's increase. When the rpm's drop down so do the RAVE valves. They work on the principle of the pressure of the exhaust system. Rpm's increase, pressure increases and the valve opens, rpm's drop pressure drops, Valve closes. They should be de-carbonized annual. To disassemble the rave valves, remove the spring clip on top, remove the black cover. There is a spring under the cover. Remove the piston by turning it with a metric socket. On the bottom of the piston is the rubber "Bellows". Be careful with the small retaining spring that holds the bellows on the piston. Remove the 2 allen screws that hold the base on the cylinder. Remove the base and gasket. The long valve won't fall in the cylinder just pull it out. There is an o ring under the base, on the shaft of the guillotine valve. Be careful to see how it came apart as it has to go back together that same way again. On the base, notice the notch that it is facing down. Clean all the carbon off the guillotine valve. I use carb cleaner and 400 grit paper. Check the bellows for any small pin holes. If so, replace it. If not, reassemble it on the clean guillotine valve, and install it back on the engine the same way it came apart. The guillotine valve only fits one way. The one closest to the exhaust pipe will come off differently then the other one. You will have to remove the allen screws and turn the base so it clears the exhaust pipe. I would do one at a time in case you forget how it goes back together again. This way you can look at the other one and copy it. Do both engines 2 per engine, if so equiped. Take your time and if you have questions give us a shout. We'll be here to help you out.
If the RAVE valves are dirty it will not rev up correctly and could be causing your problem.

The adjustment knob (the red cap) should either be screwed all the way in or flush to the top of the black ring of the cap. This will only affect performance, as far as how it jumps out of the hole or how well it runs for extended periods at WOT.

Hope this helps you understand the RAVE valve.

Karl

 

[hotrod6927]

Rave

Thanks Karl for the summary on RAVE... Quick question... When the RAVE is working correctly shold it be "leaking" water from under the black cap? Because the engine that is not running right does not leak and the the other engine does.

 

[kustomkarl]

There should be no water leaking at all. Pull them apart and check the o ring and other misc. parts of it, for a reason.

Karl

 

[hotrod6927]

Rave

ok thanks I will check it out let y'all know what I find.

After I clean the RAVEs is there a test that I can do to make sure that they are engaging properly.

 

[kustomkarl]

Just give it a run...

karl

 

[hotrod6927]

ok thanks i will hopefuly be posting good results this weekend.

 

[hotrod6927]

So I cleaned the RAVEs and they were pretty carbonized, however, the thing is still running the same way. I start it and it idles at 3000 on the drive way and then when I put it in forward and give it gas it hesitates a little and then it shoots up to 6000 RPMs with barely any increase on the throttle lever. The other engine is fine and does not do that.

I don't think its a cavitation issue since it does this when I'm on the drive way with the hose hooked up. I took the pumps off and the wear rings have some small scratches but both sides look about the same so I don't think it is that.

The week before I used just this engine to get the boat back into the dock after sucking a piece of rope into the impeller on the opposite side. Any chance that just using the one engine could have damaged something? Where should I go from here?

THANKS

 

[hotrod6927]

Oh yea one more thing when I was flushing it with the hose and running it I found a pretty descent stream leaking from the purple housing in the cooling assemble ( sorry I don't know the name of the part) Any way I'm going to fill the hole with some JB WELD. Could this leak be causing this problem?

 

[Young-SC-Owner]

Well it sounds like its leaking from the pipe....Possibly on a circle of weld? And no, that wont be the issue.

There should be NO water leaking anywhere inside the engine compt. You may replace the diaphragms on the RAVE Valves with new ones, I have seen them cause an issue like your saying....but that was on a GTX....But heck, they are the same engines.

 

[hotrod6927]

I rebuilt the RAVEs and still the same symptoms. Rebuilt the carb, new wires and found out the coil is bad. Still the revving persists...Someone said that it may be a bad rectifier. What exactly does the rectifier do. I am going to test that next, but I have to fix an air leak first bc the engine ran away on me so now I am scared to start it as I dont want to replace the whole engine. FREAKING BOAT!!!!

 

[deepdiver]

The rectifier converts the AC from the alternator to DC to charge the battery. Sometimes when it fails it generates/lets AC through which causes problems with the MPEM.

 

[hotrod6927]

ok thanks for the run down. I am waiting to get the boat on the water so I can test the rectifier. I hope it did not cause any permanent damage to the MPEM.

 

[deepdiver]

There are some previous threads re rectifier..do a search. But basically you measure the output voltage at its output with the engine running. It should be about 13.5-14.5 volts DC, and increase with RPMs. Good luck with the leak fix. Sounds like you got some relatively warm weather out there now so can still work on it.

 

[hotrod6927]

I fixed the leaks with some JB weld seems to be doing the trick. Seadoo snipe did a write up on it, unfortunately for me I found the write up after I did the repair. Anyway I pretty much did the same things that he said to do. One problem fixed just ? more to go!