96 gtx 787 typical rev problem, with a twist

[Venturian1]

This ski was given to a friend, because the previous owner could not get it to run right. I thought, no problem, bring it over, that was three weeks ago, and I'm still not getting it right.

I did all the usual stuff with the fuel system, cleaned out tank, new filter, all hoses black and flexible, tested fuel valve, check valves, rebuilt carbs with OEM kits, set pop-offs psi to max (43 psi), new check valves in fuel pump, blew brake parts cleaner through low speed holes, it came out in three places in carb bore, new base gaskets, mounted them on a spare rotary valve cover to check throttle positions to be even, etc,

So, I re-installed carbs, it fires right up, revs up right after starting, (once anyway but gets worse and worse the longer it runs, to the point where it won't rev up at all. Took carbs back off and set pop-offs at lowest setting (23 psi) no change. The injection rate was set way too high, so I thought its probably oily in the pipe, and it was,

The water regulator valve on the water box I'm not sure of tho. The spring inside is awfully stiff, would require a lot of exhaust pressure to overcome it to shut off the water being injected into the tuned pipe, its much stiffer than the rave springs, but this rev problem exists with or without water, although It idles fine, (at 3,000 rpm) until I turn the water hose on, and immediately i notice a change in sound and rpm drops. Now it sounds like its struggling, that changes to desperately struggling or only running on one cylinder, and a knocking sound starts. Shut off water, try to rev it to expel residual water, and it won't rev at all. I'm beginning to think its a timing issue, but then why would it rev up fine (but just one time) right after starting?

The CDI module is new, I swapped out the whole rear electric box with a known good one, no change. I gravity fed the carb with a gas can tied to the handle bars thinking there was blockage in a fuel hose or fuel valve, nothing changes. Maybe someone put 10-40 in the oil reservoir? I removed the oil tank, cleaned it out, sucked all the oil out of the rotary valve shaft cavity, and the inj pump, replaced the oil filter, replaced the tiny injection hoses so I could see air bubbles, Idled it on premix until no more bubbles, and it still does the same old stuff, no revs. I'm thinking crank seals now. time for a leak test. or magneto/pickup coil, or partially sheared flywheel key. Plugs are new, spark is bright, compression is over 150 on both. Any ideas or suggestions anybody? Thanks for taking the time to read this!

 

[mikidymac]

Ok, lot to unpack here...
What OEM carb kits did you use? Did you also replace the needles and seats?
Did you use new carb springs from the kits?
How did you "adjust" the pop-off to "high" and "low"?
How did you "adjust" the injection rate? All you do is align the marks on the oil pump.
What injection oil did you use?

Don't mess with the water valve on the waterbox. It is controlled by water pressure not exhaust and has nothing to do with your issue.

What CDI module did you use, aftermarket ones are junk.

 

[Venturian1]

Genuine Mikuni kits, ebay $49 ships from CA, Check valves have blue stripes on the top side. Didn't come with needle and seat, or O-ring for seat. Set pop-offs as close as I could get it to 40 then around 25 psi by trying different springs, new springs, I've got a collection. Needles didn't leak or stick. I set the idle at 3k while running on premix to purge air after the oil tank removal, and I put Marine synthetic blend, Penzoil sold at Autozone for $30 / gal. Been using it for 6-7 years now,, in all 4 skis i have without any issues.
Lined up lines on the oil injection pump with carbs set for 3k rpm, by adjusting the cable at the carb end. After purging air bubbles out of the new tiny hoses I got from Temu.. Its yellow see thru fuel hose, under $10 for a variety pack! And the stainless steel clamps / collars fit perfectly.
The CDI was changed before it came to me. Looks exactly like the old one. Yeah, there's a chance its defective too, but it has a tag tied onto it that says tested in a known good ski.

 

[mikidymac]

Ok, first things first.
Get new genuine Mikuni needles and seats.
Install the original 80 gram black springs or get new ones from OSD seadoo. Do not swap springs chasing pop-off you have to use the 80 gram springs and they do not come in the kits.

The oil needs to be API-TC rated full synthetic, Not Pennzoil TCW-3 but this is not causing your issue.

Pull off the big rubber exhaust hose from the water-box to the hull fitting and see if it is delaminating from the inside.

 

[Venturian1]

Thank you mikidymac, I do appreciate this. Someone before me has been into these carbs, the check valves were not quite round, and the China kits usually have check valves that are too large to use, so the needle springs were not stock either, and the needle's seats had O-rings too large on them, and were tight. Had to drive them out from the backside. I had the water box out, and could see inside the rubber exhaust hose, it was normal, everything was quite oily inside, due to the oil injection pump setting, that was about 1/4" off the mark.
Pop-off were not exactly even, but both were 30-35psi. Carbs back on only -no flame screen, low speed screws set at 1 turn each, it fires right up and even revvs quite well now, success!
Wrong. that was yesterday evening. this morning is a different story. revs up nice, but just once. But what has changed overnight? The air temperature is all I can think of.
The CDI module was replaced with a used part, so I check it out with a VOM, and there's a few things that are NOT as the book says they should be, Where the resistance should be infinite, its 3.2 meg ohms. in two other checks, polarity is reversed, but could the book be wrong? Usually when diodes blow they become open circuits, no?
Most of the other numbers were close, a few exact. I'm wanting to test this cdi in another ski, since the only thing I found was ebay, used, for $250.
Another option is using a MPEM from a 97 XP that I had saved as spare parts, (this ski is a 96 gtx but engines and mag wiring are the same), not a direct fit, have to pull pins and move wires around, I've done this before.

 

[Venturian1]

Thank you mikidymac, I do appreciate this. Someone before me has been into these carbs, the check valves were not quite round, and the China kits usually have check valves that are too large to use, so the needle springs were not stock either, and the needle's seats had O-rings too large on them, and were tight. Had to drive them out from the backside. I had the water box out, and could see inside the rubber exhaust hose, it was normal, everything was quite oily inside, due to the oil injection pump setting, that was about 1/4" off the mark.
Pop-off were not exactly even, but both were 30-35psi. Carbs back on only -no flame screen, low speed screws set at 1 turn each, it fires right up and even revvs quite well now, success!
Wrong. that was yesterday evening. this morning is a different story. revs up nice, but just once. But what has changed overnight? The air temperature is all I can think of.
The CDI module was replaced with a used part, so I check it out with a VOM, and there's a few things that are NOT as the book says they should be, Where the resistance should be infinite, its 3.2 meg ohms. in two other checks, polarity is reversed, but could the book be wrong? Usually when diodes blow they become open circuits, no?
Most of the other numbers were close, a few exact. I'm wanting to test this cdi in another ski, since the only thing I found was ebay, used, for $250.
Another option is using a MPEM from a 97 XP that I had saved as spare parts, (this ski is a 96 gtx but engines and mag wiring are the same), not a direct fit, have to pull pins and move wires around, I've done this before.

A week later now progress report...
I was checking the timing, and trying to rev it up a bit, to watch the advance curve, my timing light starts flickering. Its barely idling now and the timing light is flashing intermittently, and both plug wires are doing it. And, only in the morning. Mid afternoon it runs perfect now, but cold mornings it bogs down. Weird. Tested everything three times now. So I put an mpem out of a seized 97xp and it fired right up this evening, will try it in the morning now. process of elimination. No sensors or gauges are connected yet, so if it still acts up, the problem must be a wire that has broken strands, and copper expanding and making contact when the sun shines on it. I've tried another rear electric box already. Or the dess post, the start stop button always works fine.

 

[Stevie96xp]

Man o man that’s is crazy definitely sounds good a freak electric issue

 

[Venturian1]

Problem solved, runs great now. It definitely was an electrical issue, but cannot be specific about which component caused the problem. I installed an MPEM from a 97 XP in this 96 GTX, and it ran fine, cold mornings, and warm afternoon. The pin arrangements on both 26 pin plugs had to be rearranged, some removed, was a brain strain for a bit, and without any sensors or gauges connected it ran beautifully. This was using the existing start/stop, dess, buzzer, and rear electrical box, with the XP mpem hanging by zip ties in the engine compartment. This was because the the harness plugs for the mag and rear elect box were way too short. Took it out on the water, for a test run and the owner said it was great, however, this is his first jet ski, and his opinion may not be the same as mine. Very short test run, I followed with a tow rope just in case.
Now I offer him the options of buying this xp mpem for $200 (with key) not knowing which gauges, sensors, if any, will work, or buying a complete front box from ebay that was only $40, from a non running ski exact same year model, so all his gauges would be functional, maybe.
He chose the xp mpem. so now i'm tasked with mounting it up front, which requires splicing into the 96's existing wire harness. If all goes well, and it continues to gun right, I think I can safely say the problem was within the fron elect box, probably the mpem. If it acts up again, I will assume the original componects were fine all along, and the wiring was the culprit. By the way, I did unplug all the 96's gauges and mode selector awitches at handlebars during the troubleshooting but made no difference. Since His LCD gauge (info center?), does not work at all, I thought maybe something shorted out or was causing the intermittent ignition issue. Those lcd gauges don't do well or last very long when near salt water, first they fog up, then turn green inside. Not waterproof obviously.
If I discover anything different regarding this issue, I will add to this post. Maybe someone sometime will benefit from it. I want to thank everybody for your support, this forum is worth its weight in gold because of you people, thank you.
I am Don
live in Ventrura Calif
own 4 seadoos...two are 1997's, a GTi and a GSi, a 98 GS, and a 2000 GTi
Have accumulated an inventory of spare parts from 587, 657, 657x, 787, and one spare 717 complete with 150 psi.
If someone is in need, ask.

 

[artr]

Before you go through a lot of effort adapting a 97XP MPEM into the 96 GTX you might want to try one more simple test. Test to see if the 12V that the holder relay supplies to the CDI module starts to become intermittent on a cold morning start. You can put a voltmeter on the CDI 12V input or just short the 12V across the holder relay for a temporary test. I had a holder relay that would drop out when starting the ski when it was cold and it was difficult to find that was the cause. It would run fine when it eventually started and warmed up. Replaced the holder relay and never saw that problem since.

 

[Venturian1]

Thank you artr, and I did jump across the holder relay, bypassing it, giving the cdi 12V at all times, with no change at all.
I then reversed my efforts from trying to find the problem in the morning, to making the problem happen in the afternoon, if that makes any sense.
In other words, when it ran right, I attempted to make the problem reappear by swapping components, jiggling, tugging on wires etc. without success. The only way I could make it happen was to wait until the next morning and start it up. This is when it would run like crap no matter which cdi was installed, which rear elect box I had connected, holder bypassed or not, gauges and sensors plugged in or disconnected, nothing changed the missfire except air temperature. The only component I couldn't be sure of was the 96 mpem, and the wiring harness.
Adapting the 97xp mpem was mostly time consuming, and I did it at first, without changing the stock wiring harness in the ski, in case the 97 xp mpem would not work out. I just spliced the correct plug ends onto wire harness plugs I scavenged along with the mpem, and plugged into the skis peripherals required to fire it up...dess post, ig coil, start/stop, buzzer. It ran good after that, warm, cold, didn't matter, problem identifdied finally, so I reckon it all boils down to the 96 mpem or wiring within that front box. One thing discovered from all of this is not to condemn a cdi, or mpem if testing results differ from what the manual says they should be.
Only about 1/2 of the resistance values given for the cdi modules were even close, and the two cdi modules values were different from each other too, with one consistency, they both only matched the manual on 1/2 of the values. I thought i had two bad cdi modules and a good 96 mpem, going by the book. Turned out to be just the opposite. So now I have a spare DC CDI module known to be good, if anybody out there is in need!
Lots of other parts too, all older 2-stroke parts. I bought a couple of skis that got scrapped out.