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2001 Seadoo GTI, Slow Fast Slow

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2_smoke

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Hi all,
New to the forum and owning, by myself, a jet ski. I got, which I still consider an amazing deal, a 2001 gti., 2cycle Rotax with a like New trailer for $750,fresh water, one owner 20 years, consistently maintained, by him, amazing condition.

Then he got into trouble. He rebuild the carburetor. When he couldn't get it running he replaced all major ignition peace's and bought a new carburetor. After not being able to get it running he finally gave up.

We actually got her running the night we pick her up because we found out that he flipped the fuel and the vent line !! Wow ! Would tell him, but I think it would make him feel bad.

So after playing with the idle and low mixture screw she's driving fine, a little slow to take off. There's just one issue first I have full throttle, but then after a while it will slow down for a while If I hold the throttle wide open it will go a set speed but then surge to where it should be. and after running it for a while i cant et it to speed up at all. The weird thing though is that if i can hit a wave and get the ski in the air i hear the impeller speed up and that ounce i land it stays there, and I get full throttle again. If I hit a wake every so often its almost like there's no problem at all


This sounds like a fuel problem, and I haven't replaced the lines yet which is the next step, I understand how those get gummed up. I don't think though that it's an immediate fuel problem because he did replace the standard fuel filter that hangs down from the top of the engine bay, with a sizable clear bulb, and that is full all the time. But that hangs low at engine height, my next step is to find the filter that is proper but that will take a week and we're on vacation this week. Is there anything else here you all might suggest we look at??
 
First get rid of any aftermarket fuel filters!
2nd, stop riding it or you are going to blow it up from running lean. Fuel issues do not fix themselves.

Get the stock fuel filter back on and replace the element and special square o-ring.

Make sure the carb has the correct jets and settings.
2001 GTI
167.5 Main
75 Pilot
2.0 needle and seat
115 gram spring
1.0 turns Low speed Screw
0 (closed) High Speed Screw.

If it doesn't run with these settings something is wrong.
 
I have posted on a very similar problem so I thought I would tag onto your post to save a little space and we will see if we can get our jet skis running. Mine runs great on the trailers. Revs good idles with no problem. When I get it on the water, it starts and idles perfect, but I have to work the throttle to keep it from dying, once I get it to “catch” it only planes pretty slow, but like yours, if I can get the impeller out of the water it takes off like a rocket. My pop-off pressure is ~30 psi consistently. It is a little lower than the 36 psi listed, but i would think that 30 psi is within the error. @mikidymac - how can we tell if the jets and needle is correct since we are not the original owners.

Also, could this be an impeller issue since it works on the trailer? Just wondering if the pressure from the water is keep the impeller from moving like it should.
 
I have posted on a very similar problem so I thought I would tag onto your post to save a little space and we will see if we can get our jet skis running. Mine runs great on the trailers. Revs good idles with no problem. When I get it on the water, it starts and idles perfect, but I have to work the throttle to keep it from dying, once I get it to “catch” it only planes pretty slow, but like yours, if I can get the impeller out of the water it takes off like a rocket. My pop-off pressure is ~30 psi consistently. It is a little lower than the 36 psi listed, but i would think that 30 psi is within the error. @mikidymac - how can we tell if the jets and needle is correct since we are not the original owners.

Also, could this be an impeller issue since it works on the trailer? Just wondering if the pressure from the water is keep the impeller from moving like it should.
When you take the jets out it will be scribed on them but have a magnifying glass handy
 
Opened the carb again and there was a lot of gas under the diaphragm (pic 1). Gas was standing above the needle. Took the high jet out and there was no number. Just what looked like Chinese writing. It seems like a really big hole and It looks like it has been out before. Is this the right one? Or replace to be sure?
 

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The carb is supposed to have gas under the diaphragm, that is how the jets are fed.

Yes, that is the correct Genuine Mikuni 167.5 jet.
cj.jpeg
 
DANG!!!!! how on earth did you see that??? I guess experience has its benefits!!! ok. So now we know that it idles perfect. the jets are correct and clean, pop-off pressure is a little low (30psi). The rest of the carb has been rebuilt (to be honest, i didnt replace the circular check valves because they looked to be intact and i didnt want to replace those plugs). I am at a loss as what to look at next. I still think there might be a carb issue because I really have to gently work the throttle to get going. If I punch it, it just dies - but it works great out of the water. Revs perfect. Could it be an issue with the impeller or shaft? Maybe too much resistance or something when it gets in the water?
 
Mikidymac - i saw another post and it seemed similar but was electrical -https://www.seadooforum.com/threads/2000-gts-jet-ski-717-slow-to-takeoff-or-catch-water.120727/
 
I read it again and i think that one is different as in it would rev high in the water but not have speed. Mine is a dog at top end when i can get there but the impeller gets out of the water, it will "catch" and take off
 
Again.....
Rebuild the carb completely with ALL NEW GENUINE MIKUNI parts. This includes everything including the needle and seat and 100% be sure you have the correct pop-off spring.
 
Ok. Rebuilding with mikuni parts and being very careful. I am a little confused as to which carb I have - the SBN38 or 44. Mine looks more like the 44 but has the o-ring slot on the carb that goes around the little filter. It looks the same as your rebuild post mikidymac but the section that has the check valves does not have the fuel line. So the question is, if I have the print slot, do I need the damper gasket that goes on the 44? Attached picture of carb. And the gasket I am holding next to it is the one in question. Part #6 on the diagram
 

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Rebuild is done and it ran well for a few minutes and then back to the same, but this time it felt like it was missing. The ski has E3.31 plugs and checking online, those don’t seem right and they look dirty. What are the right ones and I will try them. NGK br8es? I will also try the compression testing. Weird thing is that it runs great on the trailer and not so great in the water. 2001 gs
 
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