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  1. #1

    SL750 Carb/diaphragm problem?

    Sometime lurker, first time poster...

    I have an SL750 which would go pretty reliably but sometimes at full power, it would just cut out. Sometimes down to idle, sometimes kill altogether. I've always been able to restart it. Sometimes harder than others and with various choke settings. When it dropped into idle (with the throttle mashed) I could usually feather it back into full power. It got worse over the course of the day and now it's plain bad. I've had the carbs out and apart three times to make sure there isn't any gunk in them. I'm starting to suspect the diaphragms are worn out, but I really don't have a clue what they're supposed to look like fresh.

    I'm borderline amish when it comes to carbs. I'd love opinions as to what he problem could be. Also, should a good diaphragm have some dimension/cup, or should it want to lie down flat?

    I have spark, good compression, and the fuel pump is pulsing a good column of fuel when I pull the hose off the carbs. For fun, I have the fuel system from a 95 SL750 on its way I bought off ebay, too.


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Welcome to the Hulk Tree.

    When you disassembled the carbs, did you remove the back and inspect the filters?

    How about the in line filters?

    Have you checked the fuel shut off valve for obstructions?

    Any kinks or cracks in the fuel lines? Including those inside the fuel tank.

    Any water in the fuel/water seperator?

    The diaphragms should be soft and pliable. Any cracks, tears, brittleness should be cause for replacement. HELL, just the age of them should warrent replacement.

    What 95 750 fuel system did you get? The only thing you need is the triple outlet fuel pump from John Zigler for $28.

  3. #3
    Join Date
    Jul 2007
    Cedar Rapids,Iowa
    Welcome,Xlint gave you the run-down.

  4. #4
    I did inspect the filters. They weren't bad, and now they're better. The diaphragms aren't original. The whole fuel system was serviced professionally about 5 years ago. That meant new diaphragms.

    I did pull the fuel valve and made sure that sealed correctly. No problems there.

    I changed the inline filter.

    There is no water seperator on this one. Was there supposed to be? (I know I didn't take it off.)

    The fuel lines look good.

    The diaphragms are soft, pliable, and I didn't see any cracks. They seem to have a slight bowl to them rather than laying perfectly flat. I don't know what they're supposed to be like.

    It's just a stock, used, 95 SL750 fuel system. It's complete with the carbs, manifold, fuel pump, flame arrestor, and air intake. Hopefully it's just a bolt-up. I've heard it may run rich in which case I'll want to put the main jets in from my old carbs. I'd really like to know why my current system isn't working right, though.

  5. #5
    Lake Mead Bum & BTLS Mark starflight's Avatar
    Join Date
    May 2007
    Boulder City, NV
    I just looked at the parts list, and it didn't show a water separator. It did show whats called an autocock, and if you still have it, it should be deleted. The 95 had one also( item #4). Your 93 has a strainer on the pickup in the tank. Have ya had a look at it? You really should get a triple outlet pump.

    The 95 does have the fuel/water separator. It would be good to use it.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  6. #6
    Mine does have an autocock, but it's been bypassed. What the hell is that thing?

    I don't know if the 95 fuel system has a seperator or not? I suspect it's between the tank and the pump, so I won't have it. I think I will have the 3 outlet pump, though.

  7. #7
    Lake Mead Bum & BTLS Mark starflight's Avatar
    Join Date
    May 2007
    Boulder City, NV
    The autocock was to shut the fuel supply off when the engine was shut off. It recieved a pulse like the pump gets to open the valve when running. It was a cause of fuel restrictions so a tsb was posted to remove them.
    The 95 does have the separator. Here is a pic of one on the 95 650...
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  8. #8
    Ah. I don't think I'm getting a seperator. Here's what I am getting

    Any thoughts as to whether it is my diaphragms or what the problem really is?

  9. #9
    Lake Mead Bum & BTLS Mark starflight's Avatar
    Join Date
    May 2007
    Boulder City, NV
    The separator is not included in the deal. Those are 650 carbs, so you'll need to change the jets to make it work on your 750.
    If your carbs were rebuilt 5 yrs ago w/ new diaphrams, then they shouldn't be a problem.
    As xlint89 asked, did you look at the fuel strainers on the inlet side of the carbs? Also I would recommend checking the lines and strainer inside the tank. Also, w/o a water separator, if water is in your fuel, that could cause the symptoms you are having.
    It would be good to see the tops of your pistons to see how it's been burning(piston wash).

  10. #10
    One of the first things I tried was to empty the gas tank and put new gas in. It's hard to find gas now that isn't 10% ethanol, so I would think that in itself would help prevent moisture pockets in the gas. I did check the strainers in the carbs when I tore them apart the first time.

    Would I need to rip off the heads to look at the pistons? Or is a peek through the plug hole adequate?

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