need help with carb issue??

[Mario Percopo]

I just bought a 1996 Sea Doo Challenger jet boat with single rotax engine (787?).
The guy started it for me but we could not water test it since it needed a new throttle cable.
I did compression test it, both cylinders good at 150 psi.
I replaced the throttle cable and quickly found why it was broken. The carb linkage was frozen.
I tried WD40 and worked it loose but eventually removed both carbs, cleaned, sprayed, lubed them (did not open them for rebuild).
Boat starts and idles fine. Throttle lever moves freely and carb valves (flaps) open and close freely. Here is the problem, as I move the throttle lever it will only increase rpm a little before it starts reving up and down. I replaced leaking fuel lines with clear ones. I see air bubbles coming from the line on the front carb and traveling all the way back to the tank........
Any ideas?
I was told it was running fine before the cable broke. Then it sat for 8 months.


FYI..............
I solved the problem.
The fact that my boat was running off a hose in my driveway lead me to believe their is some type of governor/limiter set on the throttle where once you get past about 3000 rpm the engine begins so surge (race up and down) if you try to give it any more throttle. I put my boat in the lake. It started right up. I put it in gear to go slowly through the idle zone. Then I punched it and it took off like a rocket. It runs fine. I don't have a carb issue. The whole thing is based on a safely measure that won't let you rev your throttle above 3000 rpm if the engine is not in gear and not under load. Once I put the boat in the lake it was fine.

 

[El Toro 33809]

Welcome to the forum.

When you say it revs up and down, does that mean it is surging? If that's the case, it may be time for a carb rebuild. What color were the old fuel lines? If that were grey, they are the kind that breaks down with the ethanol in today's fuel and will mess the carbs up. Are the clear lines you installed approved for fuel delivery?

 

[Waterluvr]

As El Toro advised, if your boat has any of the grey fuel lines left in it made by Tempo they need to be removed and replaced immediately followed by a complete rebuild of the carbs, fuel and accelerator pumps and the fuel filter changed.

This is a picture from another thread this week when one of those lines was removed from a fitting at the carb. You'll notice the green slime oozing from the fuel line as the lining of the fuel hose has deteriorated, that's what stops up the carbs on these and causes various degrees of lean running conditions destroying your motor.



Also, when the carbs are off the boat it's a very good idea to replace the two small tygon 3/32" lines that come off the oil pump to the injector nozzle located just inside the intake behind each carb. They get old and brittle pretty fast, and if one breaks it will cost you an engine. Pretty much can't be done while the carbs are installed, so well worth it while there's access to them.

Get the Shop Manual before you do much of anything to the boat, and read the owners guide available on Sea Doo's website that lists all the do's and don'ts with these boats. Things like oil requirements, never boosting or charging the battery while it's hooked to the MPEM etc. will save you some expensive grief with these boats.

 

[jhjesse]

Check your pulse line going from the mag carb/or external fuel pump and see if it is kinked, cracked, broken or loose.

 

[Sportster-2001-951C-Stock]

"I see air bubbles coming from the line on the front carb and traveling all the way back to the tank........"

Air moving through your lines will cause surging and lean running which can likely damage the engine, I would suggest a comprehensive low pressure test of the fuel system from the carburetor back to the fuel tank.

If those carbs have never been disassembled and rebuilt I'll be amazed if it can run properly.

 

[Upallnight]

Thanks for posting the FIX. All too often people come on this board asking for help, but never post the FIX afterward.

 

[Sportster-2001-951C-Stock]

Quite right, that boat DOES have the rev limiter wired to the shifter!!! Revving on trailer should be avoided, most of the others don't have that kind of rev limit feature.