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96 gsx 5620 mid range problem

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jaspruden

jaspruden

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I've been researching and working on this problem for a while. Engine starts and idles just great up to about 2500 RPM and unless I choke it or pump the throttle, the engine will die. When I get above ~4500 RPM it runs great up to my max rpm of 7000.

What I have done:
New hoses, and selector valve.
Had carbs professionally rebuilt. (2x)
Installed a set of carbs from my other 787 on to this ski and had the same issue. Carbs from this ski moved to other jet ski and they work with no issue.
Carbs linkage has been synced' visually.
Cleaned and inspected rave valves. Now set flush with top of dome. The work freely. (they are the original rave valves. Non slotted)
Installed fresh voltage regulator.
New spark plugs.
Compression in the 130's as best as I remember when I checked it last year. (a little low but not so much I should be having this bad of an issue)


None of this seems to make any difference in solving my mid range issue.

I bought this jet ski with these issues thinking I could solve the problem.

I have not messed with the water regulator. That is next if no one else has any suggestions as to what I should try next.
 
Swap the RAVE valves over from your other ski and see if the issue goes away. All of them not just the blades.
 
I'm very anxious to hear how it runs after you swap the RAVEs. I've been chasing this problem for a year now.
 
It had the slotted ones in it when I bought it, but I was having problems with them melting so I got a used set and the ones they sent me weren't the slotted ones. I can't remember how it ran after I put those in (was having some other issues then too). If if jasp sees improvement when he swaps them, then I will consider buying a new set of slotted ones. What do those slots do anyway?
 
My guess is it breaks the vacuum and surface tension to let them move once they get oily.

What is still unknown is why some skis will not run with anything but slotted ones and other skis don’t care.
 
That sounds logical to me, Who knows, but maybe I have one that cares Sorry for hijacking your thread jaspruden, bur I figure its only fair since you hijacked mine (no worries just kidding around) Please do let us know if swapping the RAVEs makes an improvement
 
I have located a set of used slotted ones on eBay. They won’t come for this weekend so I may move the ones over from my good running one. They probably need cleaning anyway. Don’t know if they are slotted or not.
 
One thing to keep in mind when swapping RAVEs around or replacing them, if an engine has been bored oversize, the RAVEs need to be ground down to allow them to clear the pistons. Before just putting them in and trying to start the engine, I recommend setting the RAVE in the slot and turning the engine by hand to make sure the RAVE is not contacting the piston
 
I was pleasantly suprized to receive my slotted rave vales in the mail today. Made my 4 hour commute and installed them tonight. I just cranked and killed it. Cant really tell anything on the trailer. Ill give it a try tomorrow.

Thanks for the tip on installing them on an engine that has been bored. Fortunately, mine appears to be stock.
 
Well launched the jet ski this morning with the newly installed slotted rave vales. No change unfortunately. I had read that the red screw should be run all the way in with the slotted rave valves. That is where I had them set.

Instead of being on the river and a public launch, I launched at a private launch today. I had time to crank it up with the seat off and look at things. I did notice that the water regulator has a drip. Guess that is my next step unless there is something else I need to do.
 
I was out today as well. I had been running with the RAVE adjustments flush with the top of the cap, so just to see what would happen I turned them all the way in. Made zero difference. I would tend to think if it were the RAVEs causing the problem it would have at least made some difference (better or worse)

I went after the water regulator too. No difference. You do want to get that leak fixed but not sure it will cure the problem. BTW the adjustment on that is supposed to be 3 turns out from fully bottomed.
 
jaspruden said:
I'm suprized there have not been any more suggestions on what to do next.....
Click to expand...
OK, time to make a guess, I guess....recapping:

You seem to have ruled out the carbs (swapping them with another ski, same problem, no change)
You seem to have eliminated the RAVE valves
We can assume the battery is not part of the issue since it starts and runs. You changed the rectifier/regulator...have you checked for steady voltage back to the battery with ski running...just to make sure the ski is producing good voltage for spark (although you say it runs good once you get it over the 4500 rpm hump - hmmm?)
You bought the ski - used presumably - with some performance issues

OK guess time: If the head has ever been taken off and the gasket replaced.....is it possible the SQUISH clearance has not been set properly or the wrong gasket thickness used???

IDK....I'm wagging on this......the only other thing to consider is the timing BUT it runs great above 4500 to 7000 rpm? so I'm stumped......

Think FAST - Fuel, Air, Spark, Timing
 
Yes it was used with performace issues. When I got it, it would not ever go above 2500 RPM. Carb job fixed that and is where I am now. I dont know if the rotary plate has ever been taken out or not. I just received a protractor to check that timing this weekend. I dont know what the performace is like when the rotary plate is out of time.
 
Found a set of carbs off a 97 seadoo that has a built in accelerator pump. I may give them a try since I seem to be starving for fuel.
 
I'm not surprised that no one else has any ideas. Everybody has exhausted all the possibilities. Someone said at one point that all 787s have this flat spot just some worse than others

You've swapped the carbs from another ski AND put the carbs from this ski on the other one and it runs fine. I've tried another set of carbs on mine too and did not correct it. Based on all of that, I doubt the carbs are the issue
I've replaced the CDI unit, the rectifier, the battery all with no change. Changed the adjustment on the RAVEs - no change, you swapped your RAVEs - no change.
I cleaned my RAVEs after I was out this weekend and rechecked the Water regulator valve adjustment, but I have not been back out since doing that. I doubt that will change anything but I'll let you know if it does

I'll be anxious to hear what you find with the RV timing, as I've been wondering about that too.

Another thing I've thought about would be the rev limiter. On some of the skis there is a wire you can disconnect to bypass that (just don't go WOT and wave jumping etc with it disconnected) Not sure that is do-able on our skis with this ignition system though. Also, not sure why the rev limiter would effect it just at that particular throttle position.
 
BTW, the rev limiter function is part of the ECU (most refer to as MPEM, but on the 96 GTX it is not an MPEM becuase the CDI is not integrated) You could try swapping that between skis and see if it makes a difference. That's about the only damned part I haven't replaced yet on mine
 
jjsinaz said:
BTW, the rev limiter function is part of the ECU (most refer to as MPEM, but on the 96 GTX it is not an MPEM becuase the CDI is not integrated) You could try swapping that between skis and see if it makes a difference. That's about the only damned part I haven't replaced yet on mine
Click to expand...

My '96 GTX has the CDI integrated into the ECU (MPEM)...even though my wiring diagram shows a separate CDI module....at some point the '96 GTX CDI was absorbed into the ECU. Believe me, I thought they hid it somewhere in the ski but MIKI set me straight.....
 
Yeah on some of the later manufactured 96s they moved to the MPEM. Another guy on here, soccerdad, has a 96 that has the newer MPEM. That's a much better setup from what I have gleaned from reading different posts. You would probably want to refer to the 97 wiring diagram for yours

Oh, and Miki will always set you straight LOL
 
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Did you try different RAVE valve housings? I was thinking you could swap the whole ones over from the ski you borrowed the carbs from. Both slotted and the early flat ones will run right with the good housings. There was a service bulletin in 97 about the issue you describe it is most commonly found in early 97 GSX's. I ask because it sounds like you may have ordered the blades by themselves. My mistake if I'm reading that wrong.
 
Matt, when you say "Both slotted and the early flat ones will run right with the good housings" am I understanding you correctly that both the slotted ones and the non slotted ones will run good with the good housings? Also,what makes the "good housings" good?
 
We would have to find a link to that bulletin for specifics but the point is that there are housings out there that will sometimes not allow a ski to jump up to high speed. I don't know how to ID them by looking at them.
 
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