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  1. #1

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    650sx not getting gas

    I have a 650sx that I am working on that doesn't seem to be getting gas. I have rebuilt the fuel pump and the carb but still having the same issue. I can get her to start and run only about 15 sec before it stops. If I feather the throttle and choke by hand then it will run much longer (only gotten to about 2min). I have tried adjusting both high and low jets but with no real change. When blowing air into the intake nozzle of the fuel pump it is really hard to force air into-is that normal? I have been told that possibly there is more of a vacuum where fuel is sucked into the pump instead of the gas being forced into the pump. Does that sound correct?
    Any ideas?
    Thanks in advance!!
    Last edited by pat8839; 01-23-2010 at 10:34 PM. Reason: new information


  2. #2
    Maulin Marto's Avatar
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    Is the fuel tank venting? Chk the one way white check valve? Air comes into the tank and should not be able to free flow back out, see the arrow on the valve. Your system will not function properley if the valve is bad. Make sure the water separator is empty too? Good luck.

  3. #3
    seaobin's Avatar
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    what you have is a pulse pump. When the 2 cycle engine upstrokes, is creates vacumn on the pulse line. This sucks fuel into the pump. then the down stroke presurizes the pump and presurizes the carb bowl. If you are not getting pressure on the pulse line, you will not get fuel delivery

    Fuel tank vent pressure
    blockd lines
    bad diaphram --my bet
    missing return restrictor

  4. #4

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    so i guess the fact that it is hard to blow through the pump is normal then-I was wondering how that worked...I will have to check and see about the gas tank being pressurized I'm not sure...what diaphram would be messed up? I replaced the diaphragm that is in the carb when I rebuilt it because there was a hole in the old one. Does the little spring under that float arm needle (sorry not really sure what the technical term is) affect the pressurizing as well? There were 3 different size springs in the rebuild kit so I used the middle size, I guess I could replace it with the old one if I needed to?

    Thanks again for the thoughts guys!

  5. #5

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    Sep 2008
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    I checked to see that the pulse pump was working and indeed when the engine churns gas does flow from the pump to the carb. This weekend the engine was very finicky and was hard to start. It would run ok for maybe 30sec then die, then start up run 10sec and die. Then wouldn't start at all regardless of how much choke (zero or pulled all the way down). Then after sitting for 2-3min it would start and run another 30sec.
    Any thoughts fellas?

  6. #6
    Pain is fear leaving your body.... rlovebk's Avatar
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    1. Check compression.
    2. Clean carb and check venting.
    3. Start at factory settings on your low/high. Starting a little rich is always good. (like a 1/4 turn)
    4. Pull fuel supply into tank and inspect. Check ALL your fuel lines. make sure no leaks.
    Good luck. I don't know settings for your carb but one of these guys will.

  7. #7

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    I checked compression over the weekend. My compression was 81-82 on both front and rear chambers. The reading was the same when the engine was hot and cold. I poured some transmission fluid into the cylindar and the front stayed the same and the rear went up to almost 90.

    I have not checked all the fuel lines, I guess I need to replace them all...I recently totally rebuilt the carb and fuel pump. The only thing I did not have to replace for the carb is the gasket that goes between the carb and the engine. My rebuild kit didn't have one and I'm not sure where to get one. The old one doesn't appear to be damaged, but maybe that's a problem?

  8. #8
    seaobin's Avatar
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    rings are hosed, you should have 130+

    time for a hone and new rings at the least

  9. #9

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    Seaobin-I figured that would be the next step. I've never looked into the rings and honestly am not really sure what that entails. Are the "rings" just a few O-rings? I saw them on sale somewhere for about $12 that comes with 4 o-rings, 2 bigger and 2 smaller.
    Thanks for the advice!

  10. #10
    seaobin's Avatar
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    Piston Rings are steel rings that go around the piston crown and provide the seal against the cylinder wall. There are usually 1 or 2 rings on 2 stroke engines and when they fail, you lose compression.

    Pull the head off the cylinder (10 bolts I think) and look into the cylinders. Take pics and post here. try to get pics of the side walls of the cylinder with each piston in teh down position. That will let us see potential issues (scoring, rust, etc)

    In addition: low compression means low pulse suction, so low fuel delivery. See the connection to your original problem?

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