2000 GTX Millenium Carb rebuild limited acceleration

[whatmot]

I have a 2000 Seadoo GTX Millenium edition with 951 rotax engine. I had problems with poor idle, and bogging down accelerating, never reaching WOT. I ordered genuine Mikuni carb kit and rebuilt carbs. Idle is 1400 on water -smooth without any hesitation or vibration. Seadoo accelerates slowly on to plane and maxs out at 4000 rpm with throttle touching grip. Engine sounds smooth with no misfiring. I did not touch the original float springs or high/low carb settings from previous. All grey fuel line hoses were replaced. Replaced fuel filter. Checked and cleaned rave valves. Blew out fuel selector and have ordered a replacement.

Thought it might be throttle cable linkage adjustment? Any ideas?

 

[2strokeboy]

Id recommend to change the screws to factory and check pop off.

 

[etemplet]

Did you remove all the parts when rebuilding the carbs? You have to verify the seat size, and the high and low speed jets, also test pop-off and pressure test the carb. @mikidymac has a great carb thread to follow. It is very helpful. Also even if you have the carbs correct the rave valves can cause an issue sort of what you are having. Good Luck !

 

[whatmot]

Did you remove all the parts when rebuilding the carbs? You have to verify the seat size, and the high and low speed jets, also test pop-off and pressure test the carb. @mikidymac has a great carb thread to follow. It is very helpful. Also even if you have the carbs correct the rave valves can cause an issue sort of what you are having. Good Luck !

Yes I pulled everything off verified the popoff with the mikuni pump gauge is set correct for both. Set the high zero and low 1.5 turns..putting back together now for testing on water.

 

[whatmot]

Yes I pulled everything off verified the popoff with the mikuni pump gauge is set correct for both. Set the high zero and low 1.5 turns..putting back together now for testing on water.

I however did find the low speed screws were different on each carb so set the same.

 

[etemplet]

What did you set the pop off ? 20-21 psi is about all you want. No More. Matt likes 19psi.

 

[whatmot]

What did you set the pop off ? 20-21 psi is about all you want. No More. Matt likes 19psi.

pops at 21

 

[whatmot]

Quick question - on the 951 carb which nozzle is the fuel inlet and which is the pulse nozzle. I got them mixed up and forgot to mark each line. I assume the fuel inlet to carb is the bottom nozzle and the pulse is the middle nozzle on the carb???

 

[etemplet]

That would be correct. the hose coming out of the side of the engine goes to the pump in the middle.

 

[whatmot]

Ok got it going idles about 3000 then takes off suddenly and I pull choke to kill it. I think I need to set the idle to 2800 rpm with idle screw. throttle now super responsive. Do I need to adjust low speed screws further (set to 1.5 turns) or just the main idle screw??

 

[etemplet]

Don't play around with a carb 951 on the trailer unless the azz end is in the water. They WILL runaway. That's why I like 2800 RPM idle. When you start a 951 it is generally lean of course, so you blip the throttle and the lean engine takes off. The longer you let it run the more likely the engine will run away. Once the RPMs start to climb... kill the engine right away. I'm not paranoid.... it has happened too many times. Good Luck !!

 

[whatmot]

Got seadoo on water. No problem with engine starting stopping. idles rough at 1400 seems to be missing. Throttle revs and returns to idle ok. took video of idle by dock. smooth then misses...Not sure what to do next? tried adjusting low speed and idle screws slightly.
One drive video with sound of idle.

https://1drv.ms/v/s!ApjnrQjsuPAewlwkxlRHLCRN3Soj
https://1drv.ms/v/s!ApjnrQjsuPAewluDTL7a0GakYa1k

 

[Grim]

How are your spark plugs? and plug wires? Is it running well above idle?

 

[whatmot]

Brand new sparkplugs. wires look ok. running between 1400 & 1600...settles to 1400 after throttle application.

 

[etemplet]

As long as the miss isn't consistent or affecting the engine RPM I wouldn't be too concerned. You can get into the weird shitznit range and spend a lot of time and $$ tryin to find those sort of things. Disassemble and clean wire harness connectors all the connector plugs. Inspect all the little wires and make sure they are making good contact. I clean that dielectric grease off. Those plugs get loose over time and I want good contact. Make sure none of the wires are pinched (that was a big problem on m1996 GTX. Wire was smashed under the rectifier. Then you can get into the coil, rectifier, plug wires, MPEM and you still might never get the miss cleared up. I've cleared up a misses by replacing the MPEM which is expensive unless you have a spare. LOL

Swap the spark plugs.... it's the easiest. New spark plugs can be defective.

 

[whatmot]

I replaced a line on the carb that had split and noticed inside the old line there is a restrictor flow valve inside..could be the issue if missing? Carb could be flooding?

 

[etemplet]

I believe the absence of the orifice in the line will allow the fuel to bleed backwards into the PTO carb. When that happens the accelerator pump will loose it's prime and when you need a shot of fuel you won't get it.... creating a bog. I don't know if the fuel flowing back would do anything in the form of flooding the carb but that doesn't mean it isn't possible. I believe that part gets left out of many carb rebuilds. Good Luck!!

On a side note I've been arguing with some new carbs on a 787 GSX. I hope I found the problem but it wasn't the carbs... it was the return line an fuel vent where I found trouble.

 

[whatmot]

Yipee!!! The little restrictor valve missing was the issue. Such a small thing could cause major problems. A couple of minor issues still to fix but takeoff, mid and top end all working great!!!

1. Got to adjust idle to 1400 - currently 2000.
2. Adjustment on low end screw as stalls when applying throttle slowly. If I brap the throttle no problem getting going.

Thanks so much for all the input and advice. I can comfortably rebuild a carb and have fun doing it! My sons are so happy!!!