2001 GTX carb will not rpm. Maxes out at 5700

[Stealth800]

Hi everyone. I’ve been a Ski Doo and Can Am guy for a long time. I’m now the owner of two 951 Seadoo’s. The one in question is a 2001 Gtx. I bought the ski in rough shape not running. Over the winter I restored the entire ski. Spared no expense. The 951 has a new WSM crank, wossner 88 mm pistons, new fuel lines, oil lines. Rebuilt the carbs, After a forever wait getting a crank for this due to Covid I finally got it running. So here is the issue. Starts and idles great. Has a bit of a bog from 1/4 throttle if u are slow to accelerate. I’m going to adjust the low speed screws for this. The main issue is it only hits 5700 rpm. Pretty much from 1/2 throttle up it just changes the tone of the engine. If I pin it from a stop it pulls hard, will flash to 6200 then drop to 5700. I checked the water valve and Raves. I ran it with the caps off and made no difference on top. It made the bottom end worse but that’s to be expected. If I add choke at full throttle it quickly starts missing so it seems fuel supply is ok. Plugs look chocolate brown. I’ve spent lots of time searching and trying things people on here have done. I have not been able to verify the tps adjustment. I’m having issues finding the pin out for the Mpem as I can’t reach the sensor connection to test there. I’ve heard conflicting info about how much the tps effects the carbs engines. The engine sounds flat at higher throttle if you know what I mean.

 

[mikidymac]

What carb kits did you use? New needles and seats?
Is the accelerator pump squirting?

 

[Stealth800]

The accel pumps work. No new needles and seats. I used Mikuni parts. From a stop it will accelerate well with no hesitation till it hits 6200 ish then falls back. Do you know if the TPS being out of adjustment could effect it this much on a carb engine? I’m trying now to figure out what pin is the TPS signal at the mpem. So I can check it.

 

[Stealth800]

Update. I was able to check the TPS and it switches from 5 volts to 0 volts at about 80% throttle. My question is if choking when it won’t rev any higher causes the engine to immediately die , even with half choke, does that rule out fuel issue? I’m going to verify the water regulator flow again too

 

[GGuillot]

No new needles and seats. I used Mikuni parts.

This is one area you want to "spare no expense" like you say. New OEM needles and seats, new genuine OEM carb kits, verify pop off, etc. The carb skis are very flakey if they're not perfect, same for the fuel entire fuel system, any leaks (sucking air) at the fuel selector, fuel filter and so forth will cause run issues.

Maybe bypass the fuel selector and see if it changes anything.

 

[Stealth800]

This is one area you want to "spare no expense" like you say. New OEM needles and seats, new genuine OEM carb kits, verify pop off, etc. The carb skis are very flakey if they're not perfect, same for the fuel entire fuel system, any leaks (sucking air) at the fuel selector, fuel filter and so forth will cause run issues.

Maybe bypass the fuel selector and see if it changes anything.

 

[Stealth800]

Ok, thank you. I will look into that. It just seems weird that choking it doesn’t help at all. Although these pop off carbs are different animals than float style.

 

[Stealth800]

Update. So I rebuilt the carbs with Mikuni Kits. New needles and seats. Pop off at 23. Verified selector is ok. Took it out, same deal but it starts better now. It will flas to 6200 rpm then drop to 5700 and go about 41 mph. Any amount of choke will kill the engine. If I get off the gas and back on it will jump to 6200 and then fall to 5700. Checked the water valve and raves. Does this have a learner key option? I’m also wondering if it could be a timing issue or incorrect prop in the jet pump. I bought this not running so I never knew it running right.

 

[mikidymac]

No, no limp mode on the carb skis.

Check the throttle position sensor, I think they kick in a 5,800 rpm and could limit rpm. The manual has the procedure to check and adjust it. It is on the throttle cable where it splits to the carbs and oil pump.

 

[Stealth800]

I verified that already. Switches at about 80 percent. But TY.

 

[Mraw]

Are you sure your raves are opening? A 951 will only rev to what you are experiencing if they don't open. You can cut a hole in the rave cap to visibly see them open on the trailer

 

[Stealth800]

I have ran it with no rave caps and from what I’ve read it should then increase rpm since there is nothing holding them closed. When I did that my low end suffered but still stuck at about 5700.

 

[POPPS]

A weak rectifier can cause your symptoms.

 

[Stealth800]

I thought the rectifier was part of the Mpem on a951.

 

[POPPS]

I hope not,,,i don't believe so.

 

[mikidymac]

It’s integrated into the mpem on some years.

 

[Stealth800]

So what you are saying is even though it became part of the Mpem they still had issues that caused the same symptoms as the separate ones before?

 

[Stealth800]

The more I think about it, this thing reminds me of a car that you need to down shift. Once it hits the wall at 5700 it doesn’t matter how much you push the trigger, the engine doesn’t respond. It doesn’t bog it just acts like that’s all it’s got. If I catch air it will rev up and go back to 5700 in the water. This is what makes me wonder if the impeller is pitched wrong. But could one loose 1300 rpm on prop pitch?

 

[Mraw]

It's possible but first I would check TPS adjustment and the water regualtor on the water box.

 

[Stealth800]

I checked the water valve and is ok. I pinched off the hose going to the pipe and ran it quick and no change. I verified the tps does switch at about 80%. Funny thing is it seems to get to 5700 long before 80% throttle.

 

[Stealth800]

Well I think I found something. Tonight I was setting up the engine to do a timing check. I found tdc and .118 btdc. I was thinking about the pipe and how it works with cooling water going around the circumference of it. With that though I realized there should be no exhaust in the water passage of the pipe. I disconnected the pisser hose at the top of the pipe and started the engine for a few seconds. There is exhaust coming out of the pisser nipple! Now my understanding is there should be no exhaust coming out of there, only water from the engine where it eventually exits at the big hose on the upper pipe. I applied about 30 psi air at the pisser nipple and I have air coming out the exhaust port at the rear of the ski along with the coolant outlet. My guess is I have a cracked pipe or manifold. The gasket between the two looks fine. Someone please tell me your thoughts. My guess is all this water in the pipe is killing the pipes ability to bounce the pressure wave back at higher rpm. This would also explain the surge to 6200 as the water flow probably lags for a second when you hit the throttle. I hope I found it. I’m not looking forward to removing that pipe though.

 

[mikidymac]

No, with no water flowing the exhaust will back-feed into the water chambers. It is very common and no indication of an issue.

 

[Stealth800]

Well tonight I pulled the pipe and found a crack in the manifold where the oring would sit against. When I put this engine together the very reputable shop told me to use a pre 2001 gasket and not use the oring even though the manifold was grooved for an oring. He said the oring is no good. So I followed his advice.He was the one who did the machine work and fitted the pistons. Now if you look at the pics I added you will see there is no way that a gasket will seal to this flange. The water was crossing under the gasket and going in the exhaust. This is a WSM gasket so I have good faith in its quality. Was I directed wrong here? The back side of the inside of the pipe is all clean from the water, it was a significant leak.

 

[Stealth800]

Pics

 

[Stealth800]

Pics

Basically even if that damaged section that broke off when I removed the gasket was ok, there would be no way that the gasket would seal the flange. You can see on the one side where the metal is all clean from the water going by. I’m lucky this didn’t put water in the motor.