Strange issue - top end

[01GS]

I have a 2001 sea doo gs 787. The ski starts fine. Idles smooth but as soon as you hit the throttle it tops out at what feels like a third of the throttle. I wait for it to plane and as soon as I hit a wave and get the impeller out of the water WHAM it takes off like normal full speed until i let go of the throttle. Once i let go it bogs again until I find another wave to suck air. Any ideas? I'm at a loss. New plugs, new mpem, new solenoid...

 

[JeremyD615]

It’s not that strange an issue really. It’s a fuel delivery problem. Your 2001 GS should have the 717 motor rather than the 787 by the way...

You need to clean and rebuild the carb/carbs (I can’t remember whether that is a single carb or a dual carb setup) using only Genuine Mikuni parts. DO NOT use aftermarket parts on the carbs! Follow the carb rebuild sticky...

Make sure if you have the grey tempo fuel lines that they are replaced with black automotive lines before you do anything else.

You’re also going to replace the fuel selector valve and the O-Ring for the fuel/water separator.

This should get you back up and running like a top...

 

[01GS]

Would that explain it being able to hit top end after a wave though? Why would getting the impeller out of the water make a difference?

 

[JeremyD615]

Because you are having an issue with the transition circuits in the carbs or an air leak. When you unload the pump and spin the motor to that higher rpm, it’s able to create enough vacuum (signal) to get into the main fuel circuit and maintain that speed. You’re running lean though, so it’s harming your motor when you do that. You can verify this by giving it a bit of choke when it’s hitting that wall. If it picks up when you give it choke, you were lean. If it kills the motor with choke, you were rich. I have a strong suspicion it’s the former though...

 

[01GS]

Ok, the possible vacuum leak would be internal in the carburetor as well or somewhere else?

 

[01GS]

Also, I just went back out and tested it with the choke. It dies out when you pull the choke...

 

[JeremyD615]

Well the fact that it dies with the choke is a good thing. It means it’s not lean... I would still go through your fuel system really thoroughly. 95% of the time when bogging or hesitation occurs like that it can be traced back to the carburetors. Causes for being rich like that would be leaking needles and seats, incorrect popoff pressure, using aftermarket carb parts, or faulty check valves. I’d pull them and rebuild...

 

[01GS]

Update: new set of plugs were put in. Tech checked the carburetor and adjusted it. Said he doesn't think it needs a rebuild. There is no change in performance. Thoughts? Do I just bite the bullet and replace the carb?

 

[benjilafouine]

I think your carb was rebuilt with the wrong parts at some point. I had a similar issue after someone rebuilt my carb: it would not transition correctly from low speed to high speed.

 

[mikidymac]

Rebuild it with genuine mikuni parts.

 

[01GS]

UPDATE: ok guys so I took your advice and replaced the carburetor with a brand new mikuni carburetor. I am still having the identical issue. I'm at a loss on where to look next.... it bogs down until you get the impeller out of the water by jumping a wave and then it takes off like normal until you ease back on the throttle and the process repeats itself.

 

[benjilafouine]

I am sorry to hear that as these carbs are quite expensive. At this point, I can see only one other thing: the timing is off on your engine. Is this ski new to you? Was it working correctly when you got it?

In 2015 I had issues with my GTI: after the dealer replaced the whole engine, the carb had been rebuilt with the wrong parts and the ski would not accelerate. My ski was also hard to start. It would stay stuck at 18 mph and if I played a lot with the throttle, I was finally able to make it go to full speed. As soon as I would decelerate, it would be stuck again at 18 mph. I brought it back to the dealer and it turned out that they did not set the timing right when installing the new engine (rotary valve). They finally fixed it. After that, I was still having issues but at least I could get to full throttle easier (but my ski was jumping from 20 mph to 30 without being able to cruise at anything between that). A new carb fixed this.

Now I am not a mechanics and I don't know your specific model but it sounds now like you have a timing issue. I should have thought of that from the beginning but unfortunately, it is sometimes difficult to troubleshoot and a few parts must be replaced in the process.

If your ski has a rotary valve, I would now look in that direction.

 

[01GS]

I have used this ski for two years without issue. The end of last year I lost spark due to a wire in the harness to the mpem getting beat up. This eventually shorted my mpem. I replaced the mpem and the wiring harness and am now having this issue. I thought at first that the aftermarket mpem might be the issue but I was told that could not be the case. I dont know if what I'm experiencing is a totally separate issue or somehow related.

 

[01GS]

I just read another forum about possible water pump/exhaust hose issues causing it to not accelerate while in the water. I went and checked the exhaust hose just now and it is fairly soft. I havent removed it yet to check for delamination but am wondering if this could be the issue.

 

[benjilafouine]

Then I don't think it is the timing unless this could go off by itself (I really have no clue). Whatever it is, it has to be obvious. You wouldn't have left a garden hose reducer/adapter in your hose port behind the ski by distraction? I was told never to leave one there while I was troubleshooting my ski four years ago.

Did you check the fuel selector valve for anything broken?

 

[mikidymac]

Wait, it’s an aftermarket MPEM?

 

[01GS]

Yes.....

 

[etemplet]

I just breezed through the thread and may have missed something BUT I had this issue. IT is a rich condition because the needle is lifting and sending too much fuel. Set the pop-off at the higher end and it should clear up some or actually all the way. Carb is dumping too much fuel and the engine can't burn it fast enough. Give that a shot.

 

[01GS]

I just breezed through the thread and may have missed something BUT I had this issue. IT is a rich condition because the needle is lifting and sending too much fuel. Set the pop-off at the higher end and it should clear up some or actually all the way. Carb is dumping too much fuel and the engine can't burn it fast enough. Give that a shot.

 

[01GS]

So would that be on the carb itself? Is it possible that a brand new carb would have this same issue as the old one?

 

[etemplet]

Ah... I Missed the part where you replaced the carb. Well you could still check the pop-off pressure. I'd expect it to be in a good range though. I find the skis run much better with the pop-off in the higher range.

So.... I have two 1996 and a 1997 GTXs. I rebuilt the carbs side by side same settings.... everything. Both skis responded almost the exact same. I tried the 23psi that I got with the initial rebuilds. Then I went up to 27 psi pop-off and they got a little better. I went up to 33psi pop-off and they were pretty good at the transition and I was cool with it. Then I replaced the needle and seat and put in the correct Mikuni spring and HOLY SMOKE there was such a difference. The ski went from ...
1. Are you giving me more throttle? I am offended that you don't like this speed. I'll just gargle with the extra fuel. You'll get the message.
2. You wanna go faster now? OK... let's see what I can do.
3. OK OK I"m coming hold on a second.
4. Ok, lets go....
5. I'm ready when you are slick... hang the hell on !

 

[01GS]

Ah... I Missed the part where you replaced the carb. Well you could still check the pop-off pressure. I'd expect it to be in a good range though. I find the skis run much better with the pop-off in the higher range.

So.... I have two 1996 and a 1997 GTXs. I rebuilt the carbs side by side same settings.... everything. Both skis responded almost the exact same. I tried the 23psi that I got with the initial rebuilds. Then I went up to 27 psi pop-off and they got a little better. I went up to 33psi pop-off and they were pretty good at the transition and I was cool with it. Then I replaced the needle and seat and put in the correct Mikuni spring and HOLY SMOKE there was such a difference. The ski went from ...
1. Are you giving me more throttle? I am offended that you don't like this speed. I'll just gargle with the extra fuel. You'll get the message.
2. You wanna go faster now? OK... let's see what I can do.
3. OK OK I"m coming hold on a second.
4. Ok, lets go....
5. I'm ready when you are slick... hang the hell on !

At this point I am looking at 3 things:
1. Exhaust hose possibly collapsing causing the ski to fall on its face only under a load.
2. Water pump failure?
3. New aftermarket mpem is bad

 

[mikidymac]

There is no water pump.

Exhaust hose is easy to pull and check.

I know others have had issues with the aftermarket MPEMs.

 

[01GS]

There is no water pump.

Exhaust hose is easy to pull and check.

I know others have had issues with the aftermarket MPEMs.

I purchased a new (used) exhaust hose as mine is pretty soft and I am in the works on getting another MPEM. I will replace each one at a time and report back. I am open to other ideas as well while i wait.

 

[benjilafouine]

I really wonder if an engine can develop bad timing. Anyone knows?