GSX 97 (787 engine) running problem.

[peter Nosbor]

The ski does not run well above 3,500 RPM. Both cylinders have spark and my mechanic tells me that the timming is not advancing.
We have checked the crank - it is true, we have checked the flywheel and associated keyway, it is as per specification.
The VTS recently blew its fuses and I have disconnected it - don't use it anyway.
Is this a problem to do with the MPEM?
What are my options - I don't fancy buying a spare unit at over $Aus 1,000 unless this is the problem.
Is there a way to test the MPEM to see if this is the issue.
I see that second hand MPEM are available.
Does anyone else have these types of problems and give advise on replacing the MPEM?

 

[kustomkarl]

What is the compression of the cylinders. If it has low compression it will act that way. Do a compression test for starters.

Karl

 

[peter Nosbor]

More info

Thanks for your prompt reply.
More info may help.
Engine hours are about 135.
It dropped a RAVE valve at 105 hours and the engine was completely rebuilt, run in as per the recommendations and ran fine since then until recently.
The engine is effectively only 25 hours old (15 if you remove the 10 hours of run in)
(The low hours is due to a new family - babies and young kids are not conducive to fun on a jetski.)
I am planning to sell the ski and buy a boat - but do not want to off load a problem onto another person.
To answer your question - the compression on both cylinders is as per specification.

 

[kustomkarl]

The compression should ideally be 150 psi per cylinder. Time is time idle or running at full bore...so it has 25 hours on it.. Have you changed the plugs also? If the mpemis bad it won't run. If you can't figure it out have a seadoo dealer check the mpem on the mpem reader.

Karl

 

[peter Nosbor]

Karl,
The Australian dealers in Seadoo need to be re-educated in customer service as they provide very poor service - even in the capital cities.
They have basically said to me the ski is over 10 years, buy a new one.....
From your knowledge, can you advise the correct part number for a MPEM so that I can chase one down. I see them advertised from time to time but I have heard the 97 GSX was a bit special one (which turned out to be a dog) and newer units are not compatable.
Your help is most appreciated.

 

[Dennis]

Mpem

I'm with KARL, I seriously doubt the running problem has anything to do with the MPEM. The next thing I would check is the charging system. Anything over 15 volts will make the engine run bad at higher R.P.M.'s
Unplug the rectifier and see if it runs good. If it does then you need a new one.
Good Luck, DAWG

 

[PWCdoc]

3500 rpms is right about when the RAVE valves open. Make sure they are clean, change the plugs and give her a try. Also, make sure they are installed properly.

 

[kustomkarl]

Another thing to check is the rev limiter switch in the controls. Sometimes it sticks and won't allow the engine to rev past 3500 rpms like when it is in neutral. Pull the controls out of the boat and check to see if it is sticking and not allowing the correct rpm. I had the same problem in my Challenger and that solved the problem. Sometimes the simplest things get over looked as it must be a major repair...

Karl

 

[PWCdoc]

His is a GSX, not the jet boat. No nuetral on the wee boats.

 

[kustomkarl]

Opps...sorry about the neutral switch... that only applies to the jet boat models. It must be the rave valve adjustments.

Karl

 

[peter Nosbor]

Some more detail and corrections.

The jetski starts first go (after priming) and idles fine.
At (and above) 3,200 RPM it starts to run rough and backfires. I had the air box off and could see the two carby mouths. The orange backfire flame (coupled with the noise) coming from both carby's was quiet spectacular.

The ski has always shown a low 12v alarm except immediately after externally charging the battery.
I have been through several batterys because the ski is often not run for several months and the battery runs flat. I now use a dry battery and have the ski on trickle charge 24/7 as per the battery's manufacturers specifications (and their recommended charger).

The VTS unit is no longer connected as it was blowing the fuses. (I don't tend to move the trim anyway - more of a gimick than a truely useful function (rather have a neutral and/or reverse).

The carbys have been cleaned out and all set as per specifications.
The stator has been replaced.
The flywheel has been removed and re-installed and the timming appears correct at idle. The timming does not appear to advance (it doesn't change) at all as the RPM increases.

RAVE valves - what can a layman check to confirm operation.

As for the rectifier - please provide soem details on how to remove and whre it is and what it looks like. Once out, how do i check the ski's operation?

I really appreciate your help.

 

[timmyboy76]

rectifier will look something similar to this..........http://www.parkeryamaha.com/seadoobombardierrectifier278001554.aspx
When disconnecting the red wire, your pretty much shutt'n down its use, if the rectifier is bad, it'll cause a "bogging" condition.
Disconnect it, then rerun the ski, if bogging is eliminated, replace the rectifier..:cheers:

 

[PWCdoc]

"RAVE valves - what can a layman check to confirm operation."

Remove the black caps on the exhaust, remove the valve and see how gunked up they are. Keep note on which side is towards the engine when you remove them as you can install them backwards. Also, let us know how they were installed so we can make sure the go back in properly if they currently are not.

 

[seadoosnipe]

Rave....

:agree:

If I might add.........I also make sure the one I take from the MAG side, goes back in the MAG side. I do not cross the guillotine valves from one cylinder to the other.

Does it hurt? Probably not. I was taught really young, always put everything back in the same place it came from. When I tear an engine down, most important bolts, like the head bolts, I put on a cardboard template and put them back in the same hole they came out of..........

I don't know.........call me OCD.........:rofl:

 

[PWCdoc]

Same bolt hole? WOW!! LOL

So, if we really wanted to mess with you all we'd have to do is sneak in and re-arrange all your bolts when you weren't looking and leave you a note telling you? Or...better yet...just switch two bolts and leave you a note:


"We switched two bolts while you stepped away"


Just messing with you my friend. lol