1997 GSX 787 stalls at 4000 RPMS

[Tickguazy]

Hey y’all, new to this forum, wondering if someone could help me. I got a GSX a couple of weeks ago. When I took her out on the water and started it, she idled great with no issues. But as soon as I gave it full throttle and hit 4000 RPMs, it stalled immediately, like someone pushed the stop button. The gauge cluster completely shut off as well. It would then fire back up with just a push of the button and run great until, again, 4000 RPMs, it shuts off the engine. Here’s what I did.

-I took out the carbs, gave them a good clean (even though the carbs were already super clean), completely rebuilt the carbs, adjusted the pop-off pressure to 38 psi
-replaced the spark plugs
-replaced the battery
-tightened down and cleaned the grounds as some of them were loose
-replaced the dess post, and programmed a new key.
-I rebuilt both rave valves
-checked engine compression at 152 psi and 153 psi
-I bypassed the fuel selector valve to see if that was gummed up inside, and all fuel lines were already replaced from the gray ones.

I put it in the water, but the same issue occurs. As soon as I hit around 3500 to 4000 RPMs, the ski just immediately stalls out. Like I said, it doesn’t bog down or anything; the engine just stops. Could this be fuel-related or electrical-related? Could the rev limiter in the MPEM have gone bad? Also, it has an oil pump delete as well, just as an FYI, so I pre-mix 50:1.

 

[mikidymac]

Sounds electrical.
Also you should be at 40:1 not 50:1. Oil injection is better on these than premix.

 

[Tickguazy]

Sounds electrical.
Also you should be at 40:1 not 50:1. Oil injection is better on these than premix.

Thanks for the reply! Good to know about the oil mix. I was told by a friend that should be the proper mixture, but I guess he was wrong, so I ended up retuning the carbs and putting a new voltage regulator in. Now the ski doesn’t die immediately, only once in a while, but now it mainly bogs down, then dies. But now we have another problem: the ski is backfiring pretty often like it’s shooting flames out of the carbs and at one point both carbs shot flames at the same time. Is this because of the 50:1 mix I’m running? I read online that the CDI module could have gone bad or even the rev limiter, and those are both embedded on the MPEM, which means time for a new computer. Any thoughts?