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  1. #1
    Hoping to progress past stuck on stupid. Grufumbly's Avatar
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    'bout dead 95 SL650

    I got my hands on 2 95 SL650's. One runs like a champ, the other was running pretty rough when I bought it. It ran better if I played with the choke, but never seemed to get past about half the RPM ( based on sounds alone) of it's twin.
    took it to a wrenchhead friend of mine - he verified fuel system was pumping and good spark to all three cylinders - They both still look like the old style fuel pump btw. So we ran compression checks on the three cylinders #1 - 0psi. #2 125, #3 80
    I haven't had a chance to take the heads off and check the cylinders yet , but I'm thinking the OEM cruddy fuel pump smoked the #1 cylinder. I don't know about #3.
    Anyone got ideas for options? I know SBT sells replacement motors for @945. I'm trying to figure options between boring the cylinders out and trying to clean them and fixing it that way, or dropping a new motor in.
    Is dropping a 750 motor in there an option without too many major mods?
    Thaks for your help in advance !!


  2. #2
    casey67's Avatar
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    Welcome to Green Hulk
    As long as the crank and rods are OK,slap some 750 cylinders and pistons in it.
    Lately E- Bay has had alot of 750 parts,shoulg get stuff pretty cheap. Good luck

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk Gruf.

    Check out my classifieds thread for a complete 750 cylinder, piston and head package. Or 780 for that matter.

    You'll need to bore the jugs, get new gaskets and rings, but will run you alot less $$ than any rebuild. As long as your bottom end is good that is...

    You'll need to rejet your carbs, swap out CDI box and stator if you want a true 750 or 780 timing. Or you can leave the 650 CDI and stator to keep cost down.

    Then you'll want to replace the impeller to keep the engine RPM in range for the added HP. 650=68HP 750=80HP and 780=90+HP

    Might I suggest looking into a 780 top end if you're serious about a swap. The HP is quite a bit more, and you'll need to do the same mods as the 750, only you'll need the 780 exhaust manifold.

  4. #4
    gorilla03's Avatar
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    xlint is right maybe a 780 might be worth it, I have a '95 750 which im thinking about changing it to a 780

  5. #5
    Water Bum Rodneyae's Avatar
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    Welcome to the HULK!!!!!!! YOu can trust Xlint. I have gotten several things off of him!!!

  6. #6
    Hoping to progress past stuck on stupid. Grufumbly's Avatar
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    Figgered out why the fwd cylinder has 0 compression

    I didn't know that 2 stroke engines were ported on 2 sides of the cylinder...and through the top of the piston.
    So here's my problems
    The aft cylinder is pushing about 80 psi. The cylinder head is smooth and unremarkable. Even colored and no knicks, dings, etc. The cylinder walls show no visible damage, and are smooth to the touch. Could this be just bad rings? the coloring insnide the aft cylinder was pretty dark.
    The middle cylinder is pushing 125 psi. I'd rather not play with it unless I have to.
    The fwd cylinder.... well, other than the hole in the piston it still doesn't look good. I've attached a picture of the cylinder head, there's a nick in it about a 64th of an inch deep. the hole in the piston looks like a through and through. I put the handle from a small artists' paintbrush into the hole to measure depth, and it bottomed out at just about an inch. I'm thinking I was hitting connecting rod/ pin. The cylinder walls show no visible damage and are smooth to the touch. Something that caught my eye / attention when I was pulling the fwd cylinder head was that it was much harder to get off, and visually, the flange on the fwd cylinder was a lot more munged up than the aft cylinder.
    The first three pics are the fwd cyliinder, the lat pic is the aft cylinder.

    Ok - Question time
    Where to from here? Replace the rings on the aft piston, and a new piston on the fwd cylinder?
    Would the hole in the fwd piston have introduced contaminents to the crankcase requiring work on that?
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  7. #7
    AKA Freeholie! I've burnt pistons like that with no contamination but you never know! you may want to pull it and do the seals also then throw some parts at it I probabl have some 650 parts to sell if u need! Z

  8. #8
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    To properly do it, you'll want to hone the cyls with the new rings. I'd re-ring the PTO (aft) and new piston klit for the MAG (front).

    BUT you need to figure out what caused the lean condition. Or it will happen again. The PTO is lean and may do the same.

    I suggest you rebuild, or the very least, go through the carbs thoroughly. Clean or inspect the fuel selector valve. Replace all the fuel lines, including those in the gas tank if equipped. Then pressure test the engine to check crank seals and gaskets.

    If you replace the fuel lines, watch for a fuel restrictor inside the return hose going to the fuel tank. It needs to be re-installed if you have it.

  9. #9
    Hoping to progress past stuck on stupid. Grufumbly's Avatar
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    xlint89 - I appreciate the help so far, and I'm sure I"ll be pinging you more . My mechanical ability is getting better by the day.
    To do what you've suggested, would it be safe to say I'm looking at having to pull the engine completely?
    I know the fuel pumps on the ski are the stock pumps. I recall reading that the stock pumps were junk, and this is a common occurance for the MAG to go like this. I know I'm going to need 2 new pumps. I have another SL650 sitting in the driveway that hasn't blown up yet. Is the dark color in the PTO making you say it's running lean?
    Last edited by Grufumbly; 03-21-2008 at 08:23 PM. Reason: misspelling

  10. #10
    you just need 1 good fuel pump not the SBT 2 pump mess

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