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  1. #1

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    SL750 carb problems.

    Ok, I tried to search for this one but had no luck.

    First a little background. I purchased a 95 SL750 new back in 95. In 01, got married, bought a house, and my wife said the ski had to go. So, I sold it to a friend of mine. He rode it for a few years, then it sat in his backyard for the last 3 years. Covered, but outside. When he put it away, he fogged the engine and put antifreeze in it. Well, a couple weeks ago I decided to borrow it back from him and get it running agian. And that's when the fun began.

    First thing I noticed is that I wasn't getting any fuel. The separator bowl wold not fill no matter how much I cranked. Reading on this forum, I decided to get the Mikuni 3 port pump, which I installed yesterday (I checked, none of the cylinders have holes in them.). Now, my fuel delivery seems to be fine, but there are only 2 ways I can get the engine started. Either pour gas directly into all 3 carburetors and start it, or hold the choke completly on. If the choke opens more than say about 1/4 of the way, the engine just dies. I'm a fairly competent backyard mechanic, I rebuilt the engine on my 68 Corvette, but I guess I don't completely understand the detailed workings of a 2 stroke engine. Put a Holley carb in front of me and I'll have no problems rebuilding it, but I won't claim to know anyting about a 2 stroke...

    So anyway, after installing the new fuel pump yesterday, last night I pulled the carburetors off the engine. What a fun job that is. I didn't realize my elbows bent in that direction... I finished that around 11:30 last night, so I haven't really looked at them. Actually, I quit before I got the accelerator cable off, so they aren't physically out of the ski yet. Anybody have any idea why the engine would only run with the choke on? My initial thought is that the reed valves could be bad, but I'm not sure exactly where they're located. If they're in the carb, that could be. But if they're in the intake, then the fact that I can run the engine by pouring fuel into the carbs would indicate that they're OK. I'm just trying to get some opinions as to what I should be looking for once I get home tonight.

    Thanks in advance for your help. This is a great forum and I've already used the information here to fix some problems....

    Bill.
    Last edited by vette68; 07-28-2008 at 09:02 AM.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome to the Hulk!

    I am fairly certain you will find the carbs need cleaning. Be sure to use genuine Mikuni rebuilt parts, or rebuild kits.

    Here is a nicely done Mikuni carburetor rebuild guide.

    Here is the 1992-1998 Polaris Service Manual.

    Now would be a good time to replace ALL the fuel hoses, including those inside the tank.

    Clean and lube the insides of the fuel selector switch (maybe put in new O-rings), to ensure you won't be getting any air bubbles in the feed to the carbs.

    Check compression, just to know you don't have any issues inside the top end. Reeds need to be in place to check compression, but the carbs don't.

    BTW, the reeds are mounted right at the base of the intake into the crank case. Once you have the carbs off, another few nuts and you can pull the rest of the intake manifolds and the reed cases off. If you do, be careful you don't tear the gaskets, or plan to install new gaskets.

    Air leaks are NOT good in a 2-stroke engine, so be sure every gasket you touch is 100% sealing when you put it back together.

    If you do pull the reeds, have a look inside the crank case for any signs of rust or water. When you turn the engine over by hand (using the drive shaft coupler), you should feel NO grittiness, roughness, or slop.

    I presume you have dumped the old fuel. Check that the gas filler and cap are not cracked, and the seal is good.

  3. #3
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Welcome to the Hulk. Sounds like its starved for fuel. Clean the carbs and change the fuel lines. The carb filters are probably gummed up. Check the fuel cock to see if its restricting flow. Bypass it for testing.
    It would be suggested to replace the fuel pump w/ a 3 outlet pump too.
    Last edited by starflight; 07-25-2008 at 09:07 AM.

  4. #4

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    Actually, I did replace all of the fuel lines. Forgot to mention that. Obviously, after sitting for 3 years, it also needed a new battery. Here's a couple other things I noticed. I'm getting a good pulse, but when I pulled the pulse hose off the fuel pump last night, it was spraying a white grease looking crap out of it. So, it seems like there was some water in the crank that got mixed with some oil. It wasn't much, but enough so that it covered the rag I put in front of it, but it's running clean now. Another thing I noticed, is when I put compressed air on the first carb (closes to fuel pump), and let it blow through the return line (which was removed from the last carb), it felt restricted. I don't know if there is any internal restrictors on these carbs, it was my understanding the internal restrictors were on the SL780's. I would have expected it to be a little more freer flowing, but it wasn't.

    As far as the gas cap is concerned, that was replaced under recall in around 1998. That's the nice thing about being the original owner; I know it's history. I got a recall notice a couple years after I bougth it, I'm guessing 1998. So, that was replaced and still looks good. Even the rubber seal looks good (I checked).

    I'm pretty sure it's not a fuel delivery problem, because when I pull one of the fuel lines off the pump, it sprays fuel into the engine compartment. That leads me to believe that everything up to the fuel pump is fine. My problem lies somewhere after the fuel pump. I wish it was as simple as a hose or filter, because that's easier to get at than the carburetor stuff.

    I was sort of figuring on rebuilding the carbs anyway, which is why I took them off. After 13 years, I'm sure things are a little gummed up.

    So, I guess the most probable culprit would be the carburetors. We'll see what they look like tonight once I get the accelerator cable unhooked and get them out of the engine bay.

    Thanks for the responses....

  5. #5

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    For those that guessed carb problems, give yourelf a point.

    Now the only question I have left is what size are the needle and seat? I can't find that in the manual anywhere. Obviously, pretty much everything inside the carbs need replacement, including the needle and seat, which were rusted in place. The only one still working was the center carb. It's rusted, but everything was still free moving. Apparently someone put the ski away after gulping a little bit of water.

    Looks like I'll be having some fun... And not on the water...


  6. #6
    seaobin's Avatar
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    looks like the carbs were half ull of water.

  7. #7
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Man those are ugly! Are You sure they are rebuildable? Can ya get the screws for the kidney shaped jet cover out? Whats the fuel inlet side look like? I dont know the size of the needle and seat, but the part # is 3140040 for the needle assy. Parts list is here... http://www.atlanticpowersports.com/f...ion_detail.asp
    I have a good set of carbs from a 95 650 that are missing the low spd jets (mains and lows would need to be changed anyhow) and the chokes. They are setup for primers. Let me know if your interested.

  8. #8
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Also, did ya find and reinstall the restrictor in the return line?
    Item #14 http://www.atlanticpowersports.com/f...ion_detail.asp

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    N&S are 2.0

    Those are ugly.......

  10. #10

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    Yeah, they'll be rebuildable. Anything can be fixed with the right amount of time and money. Right now the biggest problem is that on the leftmost carb in the picture, the screw that holds the needle pivot arm in place is competely stripped. When I cleaned it off, the head of that screw was pretty well rusted. I do have to say though, that it was a pretty piss-poor design to use steel screws on watercraft carburetors when brass would have cost about .25¢ more. Anyway, I didn't have any luck getting the srews off of that jet cover plate either. My neighbor is a mechanic and he's going to try to mig weld a bar onto the rusted screw and get it off that way. He's also going to try an impact screwdriver to get the jet plates off.

    I'll know tonight if he was successful or not. But one way or another, it all has to come apart, and he won't quit until it does. If he has to drill the screws out, then that'll be how its done. I need to know if the jets are clear or not before I put the carbs back on the engine.

    And thanks xlint89, that's what I needed to know. I thought they were 2.0, but I wanted to make sure before I ordered them and caused myself more problems. You're from Cleveland? I live in North Olmsted. Where do you put your ski in the water? I assume you ride on Lake Erie...

    I will update later when progress is made. The carbs actually cleaned up surprisingly well with some brake cleaner. I got all of the rusty scale out of them and they look pretty good now.
    Last edited by vette68; 07-28-2008 at 08:11 AM.

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