97 GSX 787, yet another fuelling thread? I dont think so

[Mitch787]

Hi guys, this is my first post here, although I have been stalking this site for over a year now. I am the very happy owner of a 97 GSX with the rotax 787 that has seen all types of riding with great results. I race motocross and am very picky with maintenance, so it has been rewarding to keep on top of things and never have an issue with the ski. It now has 109 hours on it (I bought it two years ago with 63). The ski is dead-stock except for the usual grey fuel lines out, new lines in.

The problem I have seems to have been creeping up slowly getting more and more noticeable and now is very evident. The ski starts fine, runs fine, hits around 57mph (on the wishometer) at nearly 7k revs, and is a dream! Except lately its been struggling to get over 4700 revs, about when the RAVE's open. This is obviously more noticeable with a passenger on board. If the impeller lifts off the water for a second, ie on a wave, it will spin up and then get into the revs and scream until its maxed out. If you dont hit a wave, the ski can been WOT at 35mph struggling. I then quickly close and whack open throttle and it seems enough for the ski to then spin up and away we go.

I have fully cleaned and set the RAVE valves correctly. Just finished three rides ago a full twin carby rebuild, all in brand new condtion and work great (note problem was occurring before this rebuild, I rebuilt the carbs thinking it was a fuel issue). Fuel lines have been changed, all in line and fuel filters are spotless and new. Fresh fuel, fresh oil. Everything seems to be as it should be. I have been reading a little about the water regulator maybe having something to do with this issue?

Can anyone shed some light! Thanks a lot, Mitch.

 

[Dr Honda]

Either your compression is going away... or you have a RAVE issue.

OK... I see that you cleaned, and adjusted them... but I find with an older engine... they like to be full tight. If you adjusted them "Blind" to the manual spec... that may not be good. I recommend running the red adjuster to the bottom. The reason this happens (I suspect) is that the springs get weak, and the RAVE opens premature.

Try that... and get a compression reading for us. (Cold engine, open throttle, dry cyl's)

 

[Mitch787]

Hi doc, thanks for the quick reply. I removed my RAVE valves this afternoon after work and found them clean as a whistle. I had previously adjusted them to their lowest setting for the same reason as you mentioned, although factory setting was nearly there anyway.

I did a compression test twice, and got 150 on both cylinders which I beleive to be pretty good.

I checked over the water regulator and everything was ok there, no blockages or valves working incorrectly.

Any more ideas you can think of? I'm stumped!
Regards, Mitch.

 

[Seadoobuddy]

Could this be a cavitation issue?

Bad wear ring, damaged impeller or leaking Carbon seal???

 

[Dr Honda]

Could this be a cavitation issue?

Bad wear ring, damaged impeller or leaking Carbon seal???

Nope, because the RPMs are staying low until the pump unloads. With cavitation, your RPM's will jump, and your speed will be low.



Ummmmmmmmmmm......................


When it's not reaching top RPM... and you hold the throttle open... does it try to die? Or... is there any stuttering?

Are you 100% sure your RAVE valves are closed the entire way? (not the adjustment screw... but the actual valve) If they are hanging open... it will cause exactly what you are describing. Also... are the seals OK. Is there any sign of oil leaking from the RAVE stems or piston?


The only other thing I can think of is that your rotary valve has high clearance, or it isn't in time.

 

[Rabid]

Either your compression is going away... or you have a RAVE issue.

but I find with an older engine... they like to be full tight. If you adjusted them "Blind" to the manual spec... that may not be good. I recommend running the red adjuster to the bottom.

I have the rave valve red adjustment screw adjusted flush with the black cover like as stated in the manual. Should I screw it in to the bottom? I have 157 total hours on the ski..its a 97gtx ...it runs fine or will it run better?

Mike

 

[Dr Honda]

I have the rave valve red adjustment screw adjusted flush with the black cover like as stated in the manual. Should I screw it in to the bottom? I have 157 total hours on the ski..its a 97gtx ...it runs fine or will it run better?

Mike

If it runs OK... then no... don't adjust it. If you have a flat spot in mid-RPM... than yes... turn it in.

 

[bigJake]

Hi doc, thanks for the quick reply. I removed my RAVE valves this afternoon after work and found them clean as a whistle. I had previously adjusted them to their lowest setting for the same reason as you mentioned, although factory setting was nearly there anyway.

I did a compression test twice, and got 150 on both cylinders which I beleive to be pretty good.

I checked over the water regulator and everything was ok there, no blockages or valves working incorrectly.

Any more ideas you can think of? I'm stumped!
Regards, Mitch.

Mitch, The Doc is the expert here, but I just want to verify - you say your fuel filter is clean, I had very similiar symptoms last year and my under hood fuel filter looked clean but after not finding any other problem I pulled the fuel filter out again and although it looked perfectly clean, I filled it with water and the water did not drain thru the filter. I soaked the filter in Castrol super clean for 30 minutes and she ran perfect.

 

[Dennis]

Could this possibly be a infamous 787 voltage regulator/rectifier issue?

 

[Dr Honda]

It could, but since it clears up when the pump unloads... that's probably not the problem. But... that's why I asked if there was any stuttering. Stuttering would indicate electrical.

 

[Mitch787]

Hi guys, thanks for all the responses! I am overwhelmed by everybody's willingness to help out. I hope I can do the same one day.
Unfortunately no, there is no hesitation or stuttering. It pulls hard and clean. I rechecked the fuel filter and ensured t was clean ( the water trick) and it is all good. I have pulled the thing apart and have the tank out at the moment and have recleaned and verified it's all good.
I had another look at the raves - they seem to be all fine! Opening and closing correctly and with no issues.

Maybe it's time for sydney seadoo I do their thing.
Thanks for all the assistance, especially Dr Honda!

Mitch