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  1. #1

    750SL Motor HELP!!!

    I bought a used 1994 750SL. It sat for 2 years and then wouldn't turn over. I thought it was the motor, but found it was corrosion in the wear ring which prevented the impeller from turning. Thanks to this site, I was able to remove the pump and replace it with a used wear ring! I took off the heads and inspected the pistons and didn't see anything wrong.

    I had 4 GREAT rides and then lost power. I was thinking I blew a hole in the front piston, since I had not yet put on the triple outlet fuel pump I've read about on here. The compression test showed the front and middle pistons to have 75-90 but the rear piston had NOTHING! I took off the head and it looks like a dog chewed it up!!! What happened?

    The Digital temp/fuel guage doesn't work so I wouldn't know if it got over heated? It's been in the 100's on the 4 days I rode. Could it be a bearing on the crank that blew up and the pieces got sucked up into the piston? (I didn't see any pieces in there) Something had to eat up that piston! What do I check next?

    If I need to replace the engine, will a 900 SLX motor fit in my ski? I've read about the 750 Big Bore and would like to know my options if I need to replace the motor.

  2. #2
    Moderator beerdart's Avatar
    Join Date
    Aug 2006
    It could be many things. how about some pics.

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Yeah, pics please.

  4. #4


    I have never posted pics. Hope this works! I also included 1 pic of the middle & 1 pic of the front piston. The front piston has some of the black finish missing on the top. Thanks again for all the help!
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  5. #5


    The top 2 on the right are of the rear piston & were taken at night. I took the top 2 on the left this morning (also the rear piston) The bottom right picture is the front piston and the bottom left picture is the middle piston.

  6. #6
    xplayer2885's Avatar
    Join Date
    Sep 2006
    LI, NY
    Could have been, clogged carbs or clogged water lines. DO you still have your oil pump on? Did the oil lines fall off?

  7. #7
    race24x's Avatar
    Join Date
    May 2007
    Fayette, Maine
    Correct me if I am wrong but the front piston looks good as far as piston wash but the middle looks a bit lean and the rear is damaged. Is it possible a bad fuel pump and lack of fuel to the last carb back caused this?

  8. #8


    the front piston is the bottom right picture (the one that shows the silver on top of the piston which = piston wash right?? Not enough fuel because it's the last carb to get filled from the overflow??)

    the bottom left picture shows the middle piston-which looks good to me.

    I also noticed I let the oil level get low (it had less than 1/4 tank of oil when I got home !) <----DumbA$$ move of the week!

    Think running low on oil could have eaten the piston like that & only that one? Of course that would mean I was the idiot of the week for letting my oil get low, BUT my ego could handle that better than my wallet could handle replacing the crank right now. I'm hoping I can just replace the sleve and piston. Thanks for the help.

  9. #9
    race24x's Avatar
    Join Date
    May 2007
    Fayette, Maine
    I think you have it backwards the black is lean and the spots where it is missing are cooler spots from to much fuel. You are supposed to have those clean spots about the size of your fingernail near your ports in the cylinders better to rich than too lean. To me from what I have read your middle cylinder is too lean and of course you cant tell the other cause its messed up

  10. #10
    I'm rebuilding a ski right now that has a piston like that! it was a direct result of a partial carb blockage that over heated the piston until it liquefied The ski I'm working on has bad crank bearings thanks to it not being caught soon enough and letting piston debris wash thru the crank bearings ! Z

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