Driving me nuts

[Barefoot Bob]

I have a 1997 Seedoo Challenger with the 787 twin cylinder. Fresh top end this spring with pro X pistons .010 over with .005 clearance. Ran 3/4 tank through the boat before I opend it up for the first time. 4 second the first time, 8 seconds the second time and 10 seconds the last and final before it stuck the back piston.
Removed the rear cylinder, bored .020 over and triple checked everything. Took it out for the break in and withing 2 minutes stuck the rear cylinder again. This time at 5,000 rpm. Seemed to have water in the cylinder from what I could see. Is there a way water can get into the cylinder? Maybe I should have put sealer on the exhuast gaskets? I am stumped

 

[kustomkarl]

After the rebuilds, what was the compression by the way. It could have been on the hight side and sucked in the water. It should be idealy 150 psi.

Karl

 

[Barefoot Bob]

Thanks for the reply Karl

I do think I figured it out after I chatted with a guy that is real good at rebuilding these things. He told me to send him the whole engine and he is going to go through it from the ground up. I asked him if he also wanted the Y pipe coming off of the cylinders and he said yes. That he likes to snug everything up together to keep the cylinders straight. That makes sense and I bet was part of my problem. I torqued both cylinders and then put the Y pipe on. So right there it had a chance to let water in. I may still have a bottom end seal leaking but he will find that for me when he goes through it.

 

[glenwhitt]

who is your guy

I do think I figured it out after I chatted with a guy that is real good at rebuilding these things. He told me to send him the whole engine and he is going to go through it from the ground up. I asked him if he also wanted the Y pipe coming off of the cylinders and he said yes. That he likes to snug everything up together to keep the cylinders straight. That makes sense and I bet was part of my problem. I torqued both cylinders and then put the Y pipe on. So right there it had a chance to let water in. I may still have a bottom end seal leaking but he will find that for me when he goes through it.

Who is your guy? Does he have a shop or just a favor for you? Thanks !

 

[Barefoot Bob]

I cant really give a name, but yes he does have a shop and he is doing a big favor for me.

 

[Chester]

Make sure the engine gets pressure tested before installing it and rebuild the carbs.

Chester

 

[Barefoot Bob]

Thanks Chester

The carbs are accually brand new but he wants to go through them also

 

[kustomkarl]

It sounds like your on the right track. Keep us posted on your progress.

Karl

 

[glenwhitt]

new does no mean right

I but brand new carbs on my boat just a month or two ago and the mag one had leaking needle seat.

 

[Barefoot Bob]

Well I am going to box up the whole thing

I will let you guys know how it turns out. Thanks for all of the suggestions

 

[Barefoot Bob]

Well he has the motor apart and told me he didnt find anything out of the ordinary. He was hoping something would be obvious but nothing yet. He still has to go through the new carbs to check them out

 

[Dr Honda]

You said you had a new top end… did you do the bottom? I have a gut feeling that you may have a seal leak… Or… your crank is twisted just a little. When that happens, you get a few more degrees of timing in the rear cylinder.

Even with that said… since you also said you had “New carb”… did you actually check the jetting? They don’t always have the right jets in them. Also, SeaDoo (and others) like to have a larger rear main jet to keep heat down in the rear. Group K has a good write up about that.

 

[Barefoot Bob]

Thanks for all the advice. I only did the top end, the guy in Florida that has the motor is doing the bottom end and carbs. He is checking everything for me but just hasnt hit it on the head yet. I will pass on all the info, thanks again

 

[Barefoot Bob]

Well here is the problem causing the lean condition on the one cylinder.

 

[glenwhitt]

Well here is the problem causing the lean condition on the one cylinder.

wow. that will do it. I have read things like this before so after? I do any work on the carbs or rotray valve i put it on a hose, get it running at a steady rpm, and soak the area down with wd40 to see if i get a drop in rpm. so far so good

 

[Barefoot Bob]

Well I went out to break in the new motor and I was exited to say the least. The guy that did the complete rebuild for me is a very experianced jet ski builder and racer. He went through the complete motor and carbs. Even though the carbs were purchased new last year. He still wanted to make sure everything was just right.
I was very bummed out when I found out this thing has the very same simptoms as it did before I sent it away. I figured for sure we had the problem licked since the rotory valve was causing a big vacuum leak.
The thing it does is right after you take off and get it on plane is drop the rpm down to nothing. Unless you stay in the throttle and run the crap out of it (6000 rpm or higher) And the only way to get the rpm back up is to bring the throttle back to the idle postion real fast and crack the sucker wide open again. I am stumped