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  1. #1

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    94 SLT - Hole in piston

    History is kinda long, but I figure the more details, the better.
    I got this ski. It had 120lbs compression in each cylinder and ran ok at best. Took it home and decided it was time to read up on this model.
    Changed every fuel line in it. Changed all oil lines. New oil and fuel filters. Upgraded to the 3 outlet fuel pump, I did verify the return line restrictor is in place in the new line. I also plugged the port on the pto carb where the auto-cock was (I removed the auto-cock). Rebuilt all 3 carbs using Mikuni kits. Synced them using drill bit method over several iterations and set the adjusters to factory specs. Cleaned and lubed the fuel selector valve. Took it for a spin. Ran terrible. I found mag cylinder wasn't firing. Traced back to the coil/wire connection. Replaced that and all systems go.
    Took it to the lake. Ran absolutely great. Very responsive. While I was taking the 100 yard bursts to check top end rpm/speed, I noticed if I open it all the way it would run around 6100-6200 rpm, but only for a bit. Then it would slowly drop rpm. It would eventually die if I stayed in it. However, if I let off the throttle when this began to happen, it would idle fine and I would wait for a bit and go again. Same exact thing would happen. If it kept it at 5500-5800 it would eventually happen again but it took a lot longer. I assumed it was running out of fuel. I made my way back to the dock to open the high speed adjusters. I rode about half throttle on my way back for fear of something happening. Got back and backed out the screws 1/8 and it never ran right again. Played with screws here and there but made no difference. Took it home and found pto cylinder has a hole in it. I assume it happened on the way to the dock but since I was at part throttle, I really didn't notice.
    Now I read what I could find on here about it and I have two guesses but would like your inputs as well.
    1. Crank is out of phase
    2. The factory specs were too lean and it happen to get the rear one first
    The rear plug was pretty black when I got it so I cant get a fair read on it (I should have replaced it before I rode, but I didn't). The other two were new. They currently read maybe a little lean but not that bad really. Also, the rear plug was an NGK8 while the other two are NGK7. All three gapped at .027.
    The last bit of info that might help is something I just discovered might be a contributing factor. I don't know what the flame arrestor and its cover looked like from the factory, but I've read references talking about its boot and to be sure to point it a certain direction. Mine doesn't have a boot. It's a blue plastic cover with the hole pointing backwards - nothing else. Could this have allowed just enough extra air that the factory spec on the carb was too lean? I haven't seen the boot so I can't really speak to that. I am prepared to put a piston in it, but I refuse to just replace and go. I have to figure out what caused it or I'll just park it. Any input would be greatly appreciated.
    Thanks in advance.


  2. #2
    BlueFishCrisis's Avatar
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    Good to check crank phase. I would be more concerned that there is a leak in the crankcase. Need to perform a leak down test and ensure it will hold vacuum. If not, you will need to find the source of the leak. Most likely is the crank seals. These are not expensive, but require removal of the motor from the hull, removal of the flywheel and magneto, and removal of the bed plate to replace.

    The rubber boot missing may have added a bit of air, but not enough to force the motor to run that lean.

  3. #3

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    Can this be done with the bad piston still in there? It would almost seem to me that it could be done through any cylinder since it is the crankcase I will be checking.

  4. #4
    BlueFishCrisis's Avatar
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    You can do the leak test with the bad piston in there. I have done it with NO piston in there.....!!

    Need to remove carbs and exhaust pipe, then plug the exhaust manifold and the three intake locations.

  5. #5
    BlueFishCrisis's Avatar
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    Use the pulse line to pull a vacuum.

  6. #6

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    So, do the leak down with vacuum instead of low pressurized air?

  7. #7
    BlueFishCrisis's Avatar
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    I guess you could do either, but the plugs in the manifolds "hold" better under a vacuum as they are pulled in vs. pushed out....

  8. #8

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    I guess I'll read up on my leak down kit. I've never opened it...

    Thanks again. Sounds like a winter project

  9. #9

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    Ok so what is the secret for removing the exhaust pipe while the motor is still in the ski??? I tried calling it every name in the book, but even that didn't work. I have all bolts loose and the water line removed but no matter how I twist and turn it, it refuses to come out.

  10. #10
    BlueFishCrisis's Avatar
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    Take the exhaust mount bracket off of the front flywheel cover. Remove the MAG spark plug. It will come out by sliding it forward twisting, and pulling it over the MAG cylinder. Unfortunately, can't give you a better description. However, all you really need to do is gain access to the top of the exhaust manifold to pug it, if you are just trying to accomplish a leak down test. Why do you want to fully remove it?

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