1998 gtx limited rpm flat spot

[Triorieel]

Steps taken:

September:
-Purchased seadoo, compression was fine, expected carb job would fix the issue I saw.
-seadoo has rpm flat spot somewhere around the 4000-5000rpm range. If I tried to ride in that range, the seadoo would surge up and down on it's own.
-Winterized

May-June:
-fixed exhaust leak
-new spark plugs
-tried aftermarket carb kit...waste of time and money, couldn't do anything but idle

July:
-did proper mikuni carb kit and replace needle, spring, arm, etc...
Just got back from a water test.
-Has flat spot at 4800-5400 rpm range. It doesn't surge anymore, I just can't hold it in that range.
-It doesn't have the same pep as my other similar seadoo.
-Runs at a max of 6400rpm (roughly 50mph).
-1 out of 5 take-offs it is rich with fuel (hesitates for a second then takes off). I think I blame the accel pump for this. slow take offs are fine.
-using choke on takeoff is immediate stall.
-I did the compression in May. I can't find my previous post, but it was roughly 143psi for both cylinders.

Not sure where I go from here.

Edit:
I do have a sister seadoo that is waiting for a bendix to arrive on Monday. If something can be easily swapped for testing I can do it. Although one is a 5837 and the other is a 5842 (I tried getting the same but didn't know there were some differences in the same year).

 

[JJinSC]

How are the RAVEs? Have you inspected/cleaned them?

 

[Triorieel]

Nope, Nothing done with them, are those the exhaust ones that hide behind the plastic caps on top of the engine?

Edit:
Looking at the parts breakdown, do you mean the reed valve or exhaust valve?

 

[mikidymac]

Nope the ones with the black plastic caps on the cylinders. The rpm range you are having issues with is typically when they kick in. Pull them out and clean them good. They will probably be covered in thick black carbon.

 

[Triorieel]

They seemed to have easy movement in the engine (pushing up and down on them).


They are covered in wet oil.
When I did the carb kit, I noticed the oil pump spring wasn't hooked up correctly (giving lots of extra oil). I have properly adjusted the oil pump and have run the seadoo for 20-30 minutes before removing these rave valves.



Cleaning step of rave valves:
Left side dry towelled only (carb cleanered after), right side carb cleanered.


Brass wire brush with dremel:


Next step:
Reassemble and water test

Thoughts:
The rave valves had a few nicks in them.
If this fixes my problem, the engine is extremely sensitive to oil coated valves.

 

[JJinSC]

They actually looked alright. That may not have been your issue.

 

[Triorieel]

Just got back from the water test. Still the same.

The seadoo goes 6400rpm one way and 6500rpm the other (wind I guess). This is about 50mph. It still isn't as peppy as the other similar seadoo.

I have to take a 5 minutes trip out of the channel to hit the lake.
During this 5 minutes, if try to gun it, the engine wants to hesitate.

Once I hit the lake, I have to slowly throttle it to WOT. I take a quick tour. At this point, I can idle then gun it without the major hesitation, but there is something going on at the 2500-3000rpm range. There is a small hesitation passing through this. If I hold it in that range and go WOT, I get hesitation again.




Side note:
A lot more people on the water today. Not as fun when having to dodge everyone. I guess this is what happens when you finally get a non-rain day in a limited summer season area.

 

[JJinSC]

Check the water valve on exhaust. It may not be opening and letting pipe dry out. This could create a little too much back pressure making it hard to come off idle. Make sure bellow is not leaking and all is well in it.

 

[Triorieel]

Still looking for the water valve.

bellow...are you talking about what is around the drive shaft at the hull? if so that is fine.
bellow...are you talking about the exhaust copper ring thing? I fixed that when I did the carb rebuild.

what about the blow by check valve like in the video @ 24 seconds assuming I have one:
[video=youtube;6JFgzFoxuNc]https://www.youtube.com/watch?v=6JFgzFoxuNc[/video]

Am I suppose to be able to blow into the engine, or suck from the engine?

I wonder if my pressure/vaccume valve control work. Should I try swapping that with the one from my other seadoo?

 

[JJinSC]

There is a valve on the water box at the opposite end of exhaust pipe from engine. It will have a valve that looks like your RAVE valves.

 

[Triorieel]

It's supposed to be rain free in the morning, I will inspect it and report back.

 

[mikidymac]

Hold on! That aluminum check valve is not OEM! Where is it connected? If it is going from the engine case to the carburetor that is your problem. What was it connected to?

 

[Triorieel]

Hold on! That aluminum check valve is not OEM! Where is it connected? If it is going from the engine case to the carburetor that is your problem. What was it connected to?

If you are talking about the video, thats not mine. I saw a check valve in the video and figured I would start looking for the equivalent on mine and test it.

 

[mikidymac]

Ok. That makes more sense.

 

[Triorieel]

The water valve is able to freely move.

I don't know what the white adapter is with the red cap at the bottom of the picture.


I'm wondering if I can bypass that control.


Just to verify, the engine adds air into these valves to control them (because the caps have springs that push them down).
Would it be ok? if I just pressurize the valves so they are open and test them? I would like to think it will be a dog taking off, but would let me know if they are whats holding me back on the higher end.

What would you guys suggest at this point?


Edit:
...or maybe control that valve myself by giving it voltage with a switch in my hand instead of relying on the computer.

 

[JJinSC]

The white piece with the red cap looks like a flush kit. Since I am not as familiar with the RAVE valves with the vacuum/ solenoid etc. I will have to let one of the others more familiar with those chime in.

 

[Chester]

Pinch off the black hose from the water regulator and go for a quick ride. Just ride long enough to see if you get over 6700 RPM as the exhaust will overheat. The spec is 6750 +/- 50 RPM.

Chester

 

[Triorieel]

If thats the black hose on on top of the grey hose on top of the water valve. I will try it out.

Thanks

 

[Triorieel]

Played with it today and was able to change the max rpm but not the flat spots.

Things I did:
-Played with carb low adjustments fixed the take off issue and rpm's now go to 6840 but flat spots still remain.
-Played with carb high speed adjustments. No Difference.
-Removed large spring from rave valves. No Difference.
-Tested pressure line from engine to rave valves. It allows air out of engine but not going in.
-Removed large spring from water regulator...drove out 200 meters and back. No Difference to the ride, but smoking something internally. Quickly reconnected spring and took for a quick ride to cool things down. I figure this was the same thing as blocking the line.
-I tried adjusting the both carbs off from each other in each direction, it didn't do much except slow down the max rpm's a bit.
-I tried adjusting the red screws on the rave valves and water regulator. No Difference.

Recap:
-Engine now tops out at 6840rpm (I feel it should do a bit more with 142psi compression, but I know it is with in range now)
-Engine won't run between 1600 and 2000 rpm.
-Engine has problem running at ~3000 rpm (bogging or hesitating).
-Engine won't run between 4800-5400 rpm.

I must now become an expert at reading plugs to know if I am lean/rich.
Fixing those rpm ranges may give me a bit more oomph on the peak rpm.

I'm not sure what else to try, I bought a used carb coming this week. At least I will have a spare if it doesn't fix the problem.

Anyone have more suggestions to try?

 

[JJinSC]

At this point, I would recommend pressure testing the fuel system. Follow procedure in manual for fuel delivery system and carbs.