97 GTX Hitting Rev Limiter?

[mrsmith988]

I'm trying to figure out what I've got going on with my 97 GTX. Close to and at WOT gives me what I can only describe as hitting a rev limiter.

I've recently replaced the wear ring, carbon seal/boot, and voltage regulator. Seems a bit better but the issue is still there. I'm running an ArielTek MPEM as well.

I'm thinking that the motor is out of alignment causing cavitation at the carbon seal, I have the MPEM timing set incorrectly (think I'd be having other issues as well), or there is some type of fueling issue. I'm at a loss...

Here's a couple videos showing what is happening:

 

[racerxxx]

Check to make sure nothing got caught in the grate area.

Did it did this before? Ski new to you?

 

[mrsmith988]

The ski didn't do this before switching over the to the ArielTek MPEM. The original MPEM fried because of a bad regulator.

I was originally guessing cavitation because I unbolted the motor to inspect the stator to see if it had caused the charging system to fail or if it was just the regulator that had gone out. I don't have an alignment tool so it's probably not perfect (however, no water enters through the carbon seal while riding).

I took over care for the ski from a family member this year so I don't have a ton of history with it.

 

[mikidymac]

I know that most of the aftermarket MPEM's are junk.

Now if the ski ran fine and the only thing you have changed is the MPEM, then it is the aftermarket MPEM causing the issue.

I would get a good tested used MPEM form Nick or Jess at Westside Powersports.

 

[mrsmith988]

So I took a closer look at the the engine block and realized I had the timing on the MPEM set incorrectly. It was set to 2° and should be set to -1°. I'm wondering if the timing advance was overpowering/pushing the motor out of the correct parameters and causing the rev limit.

 

[AKnarrowback]

My favorite check, for bumping the rev limiter in a straight line going wide open, is damage to the trailing edge of the impeller. If the rear tips of the impeller are bent forward from rocks going through the pump then you can still have good low end performance but over rev at wide open throttle. Even with a perfect wear ring a bent impeller is still going to kill machine performance.

What rpm's are you at when the rev limiter kicks in? A stock rev limiter, according to the shop manual, for a 97 GTX is set at 7000 +- 50 rpm's. My 97 gtx holds a steady 6850 with a clean impeller and liner.

I do not have any experience with aftermarket mpems to offer any advice there.

Just as a note. I replaced my carbon seal assembly with an "old school" double seal bearing assembly out of a 94 gtx, 24 bucks on ebay, due to constant water buildup in the hull. The assembly using the 94 tube/hose to attach to the hull rides on the stock 97 shaft without interference from the o-ring groove used for the hat.

 

[mrsmith988]

It's bouncing between 6.5 and 6.6k RPMs. I've got a feeling it's the aftermarket MPEM. I'm going to try swapping a buddies OEM MPEM in to see if the issue goes away.

 

[AKnarrowback]

Yes. That seems too low.