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98 gtx rfi misses between idle and 4500 rpm

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eparker

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Hi,
Im new to the forum but have a problem. 1998 gtx rfi misses or lopes under a load from after idle to about 4500 rpm. Then it runs great. It smooths out when the rave valves open I guess. Could it be an issue with the exhaust ?
I replaced the tps and plugs and the filter on the bottom of the fuel pump.
Now I am at a loss. I know you have to be smarter than what you are working on but this one has me spun out.
Any one have ideas......???????
Thanks Eric
 
Welcome to the seadoo forum Eric. You might want to check the RAVE valves to see if they need cleaning. Here is some info on the RAVE valves Your rave valves use a solenoid to operate them.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 hold 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. 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.

Karl
 
Rave valves seem to work

The engine misses or lopes until about 4500 rpm when the valve open it take off and runs great.
The valves were clean when I put in the new engine about 10 hours ago.

Do you think it is the exhaust?

Thanks,
Eric
 
Eric, check the adjustment of the rave and see if a little adjustment helps. Be sure to keep them the same turns out.

Karl
 
it could be missing and loping because the raves are open all along. then smooths out because it is in the range where engine works with what it has for exhaust flow.
 
think outa the box

You may have an obstrruction in one of the carbs low speed jet, so when you rev up, the high speed jet evens out fuel delivery.
 
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