speedster 787, not reraching full RPM's

[Fletcher]

I have a 1999 seadoo speedster with the twin 787's. Left engine runs perfect, starts easy, idles perfect and run about 67-6800 RPMS. Right engine is a little difficult to start but idles ok and only runs about 5700 RPM's. It kind of hesitates on take off and sometimes dies.

Plugs are brown, compression is 115 on all 4 cylinders, ( I operate the boat at 6500 ft elevation) No excessive oil usage or leakage in the crank that I can see or tell. When I put it on the trailer I noticed a oily residue all around the exhaust on the back of the boat by the jet. Left side is clean.

Should I look at the carbs, or the RAVE valves first? Previous owner said he never cleaned or pulled the RAVE valves as he didn't know what they were.

And suggestions to get me off on the right start?

 

[XP 787]

Compression is low. Try another gauge. I cant see both motors having the exact low compression like that.

 

[Fletcher]

Compression is low. Try another gauge. I cant see both motors having the exact low compression like that.

That's what I thought. But after reading about how compression changes based on elevation I figured it was good. I read online that compression drops 3% for every 1000 ft gain do to thin air. So if I add 18.5% to my 115 I get about 137 which should be good. Even at this elevation the left motor runs perfect and the boat will hit 45 in choppy water.

 

[Fletcher]

really, 41 views and no advice, not even a confirmation of the compression drop due to elevation? I am going to start with the fuel filter, then RAVE valve and last is the carburetor.

 

[XP 787]

Not too familiar with compression drop at higher elevations, but after some research it sounds like you are correct. If both motors have the same compression and one runs fine im leaning more towards a fuel issue. On takeoff if one engine stumbles or cuts out it could be clogged accelerator pump nozzles. Remove the airbox and look down the carb throats. You will see 2 little nozzles with small hoses going to them. Follow the hoses to the accel pump. move the lever by hand and the nozzles should squirt fuel. Had this same issue on my boat. They have nothing to do with loss of rpm though. Go thru your carbs.

 

[BoLongo]

I have the Challenger 1800 with twin 787s. I was having an issue with one engine. Would start ok but out of the hole, it would die. I figured the issue was with the pop-off pressure, not opening. If I pumped the throttle when I throttled up, it would open the valve, and it ran great once out of the hole.

I rebuilt the carbs and took them apart a couple of times. The pop-off pressure was right. I finally gave up on the carbs and bought a used pair off eBay. Switched some of the newer parts and all is good now. For some reason, the old carbs had an issue that I could not find. But a used pair solved the problem.

Sound like you just need to rebuild the carbs and look into adjusting the jets for the higher altitude.

Only use OEM Mikuni rebuild kits!

 

[Fletcher]

Great advice guys, thanks. I will dig into it from there on!

 

[Fletcher]

Took the boat out today, right engine that I was having trouble with is now hitting 67-6800 Rpms but has a bag bog off idle. If I run it hard , then stop and go WOT it takes off like crazy and runs fine. If I idle around and for a period of time then hit WOT it will bog and die. Pretty sure it's a fuel issue. I haven't dug into as life is busy but plan too this week. Man this boat really moves! Scared the crap out of the wife today! Also right engine takes a little fitness to get started.

 

[ialonso]

... but has a bag bog off idle. If I run it hard , then stop and go WOT it takes off like crazy and runs fine. If I idle around and for a period of time then hit WOT it will bog and die. Pretty sure it's a fuel issue.

Sure sounds like it. Leaky something (needle seat or something else..)causing excess fuel to be dumped in.

Carbs are tough to troubleshoot. Rebuild it perfectly, or replace it. They run Great for a long time once the carb is perfect as long as you feed it CLEAN fuel.

Best of Luck!