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  1. #1

    SL650 Bogs at > 1/2 Throttle

    Hi everyone, new to this great forum. I picked up a 1994 SL650 and working to improve it. Have searched as best I could and still have a couple questions. All new fuel lines, rebuilt carb, compression is 110-118 psi in all three cylinders. Having the problem obtaining high RPMs; motor stalls above ~ 1/2 throttle. Running at sea level, adding some choke (not full) allows the engine to spin up properly. My questions are these:
    Will turning out the high speed carb needles give me enough fuel to alleviate the problem?
    Does each carb need the same adjustment or do I start with #1 and test each setting? (and can someone tell me why the high speed needle adjustments are different for each cylinder).
    Finally, what are the advantages of the Triple Outlet Fuel Pump vs rebuilding the stock pump?

    Thanx for an AWESOME site.

    Stu


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by StuZ654 View Post
    ...1994 SL650 and working to improve it. Have searched as best I could and still have a couple questions.

    All new fuel lines, rebuilt carb, compression is 110-118 psi in all three cylinders.

    Having the problem obtaining high RPMs; motor stalls above ~ 1/2 throttle. Running at sea level, adding some choke (not full) allows the engine to spin up properly.

    ...Will turning out the high speed carb needles give me enough fuel to alleviate the problem?
    Does each carb need the same adjustment or do I start with #1 and test each setting? (and can someone tell me why the high speed needle adjustments are different for each cylinder).
    Finally, what are the advantages of the Triple Outlet Fuel Pump vs rebuilding the stock pump?...
    Welcome to the Hulk!

    The triple outlet pump ensures you have more than enough fuel flow and pressure at wide open throttle (WOT).

    The stock fuel pump is OK (just), but as it ages, it becomes less effective. The reduced fuel flow can cause the carbs to starve for fuel pressure at full power. Since the triple pump is not very expensive, there isn't much point to just rebuilding the single outlet pump (but it is OK to rebuild it, if you prefer).

    Since you changed the fuel lines, did you make sure you still have the restrictor in the return fuel line?
    I think in the 650, the restrictor was a small brass slug inserted inside the return fuel line, near the last carb. It has a tiny hole through it, to create back pressure by restricting the fuel return flow.

    Without the restrictor, you will not have proper fuel pressure (about 4PSI at wide open throttle, 2PSI at idle).

    Insufficient fuel through the carbs (low fuel pressure, incorrect carb settings, dirty carbs) causes the piston temperatures to rise, melting a hole right through the top of the piston. Too often, you don't even notice the problem until the piston completely fails.

    Typically, you would adjust all three carbs together, to increase the fuel flow at high speed. Depending on the engine tuning and exhaust configuration, some cylinders need a little more fuel flow than others to run at the proper temperatures. This is why the carb settings can be different from one cylinder to another.

    Note that turning the carb screws OUT too far can result in poor performance, but no danger of engine damage. Running at full throttle with the screws too far IN can also cause poor performance, but can ALSO quickly damage the engine from lean operation, and high piston temperatures.

    Are the carb screws currently set at the factory settings?

  3. #3
    Thanx for the response. Yes the carbs are set to factory settings. Fwd 7/8, Ctr 1/2, Aft 3/4. Return line has the restrictor. I will try adjusting the high speed needles richer and see what happens. In the mean time I'll order up the new fuel pump as well. Thanx again.

    stu

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Did you inspect the fuel shut off valve?

    Did you inspect the in line and internal (back of carbs) fuel filters?

    May need to do a leak down test.

    And welcome to the Hulk.

  5. #5
    ph2ocraft's Avatar
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    I'd also like to say WELCOME to the Green Hulk Forums!!

    Pinch the return line closed, if the engne runs better to very good, you know you have a fuel pressure issue. SHORT, WOT burts only. If you're running lean you don't want to burn her down.

    What are your MAX RPM's
    Have you checked the piston wash?

  6. #6
    Thanx for the responses.

    I will try more troubleshooting. I do not have a tach and the Piston Wash test is something I need to learn. If I were to guess, I am spinning ~ 3000 rpm at WOT. I opened the high speed needles a 1/4 turn at a time. It took a FULL turn to keep the ski from stalling at anything above 1/2 throttle. With the needles that far open, the engine would not stall at WOT, but RPMs were low. At stock carb settings, with some choke, I can get full RPMs (guessing). Sounds to me like a fuel volume/pressure issue and not a mixture issue. I'll try the pinch of the return line. Sounds like a simple test for the pressure issue.

    I have an order with John Zigler for a new triple outlet fuel pump. Will eliminate the pump as a problem.

    Thanx to everyone for pointing me in a direction.

    Stu

  7. #7

    I'm no expert.....but

    my experience has shown that when you have close the choke for a 2-stroke to run, then 9 times out of 10 the carbs needs cleaned and/or rebiult.

    Just my 2 cents

  8. #8

    Factory carb tuning

    Does anybody the factory carb adjustments for a 94 polaris sl650
    Thanks

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by Codered346 View Post
    Does anybody the factory carb adjustments for a 94 polaris sl650
    Thanks
    What you seek is in the tech section.

    http://www.greenhulk.net/forums/show...t=15473&page=2

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