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Thread: Bad fuel pump?

  1. #1

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    Bad fuel pump?

    97 wvt1100.. Newly rebuilt carbs, ran great after first tune. Put on a new throttle cable, took it back out, when I get to about half throttle ski shuts off. Need to prime it to start it back up.

    If I idle for about 30 seconds then gun it, I can get pretty far until it dies again, my thoughts on this is because the carbs are loaded with fuel already?!? If I only pull the throttle in about 25% I can get up to about 30mph and it runs fine untill I punch it, or even if I slowly increase throttle over 25% it then dies pretty abruptly. Plugs look fine, possibly even a little lean.

    Does this sound like its leaning out? I did blow air into the fuel pump @ 80psi, (which I was told is horrible for the pump), but like I said that first day it ran fine.


  2. #2

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    Just off the cuff I would say that 80psi is excessive. I can't, however, explain why it ran after that if it incurred damage.

  3. #3

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    Well I pulled the fuel pump out, and the top plastic ring had a small crease in it, could this be the issue?

  4. #4
    If you're talking about the diaphragm (the big plastic circle), I wouldn't really think the crease would have that much of an effect (as long as there isn't a tear) since it would still be able to move back and forth. If you're talking about the check valve (the small plastic circle), it could definitely cause an issue since it would allow fuel to travel in both directions through the pump.

    Edit: I fully expect that someone will argue with me about the diaphragm being creased, but it seems to me like it would still be able to "pump" even if it had a crease (although ideally of course you don't want it to be creased).

  5. #5

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    I'm talking about the two small plastic circle pieces with the rubber in the middle of them.

  6. #6
    Quote Originally Posted by bryan428 View Post
    I'm talking about the two small plastic circle pieces with the rubber in the middle of them.
    Those are the check valves - they make sure fuel only travels in one direction between the two halves of the fuel pump - so I could see your motor potentially being starved for fuel (it could create a loop inside of the fuel pump where the fuel never makes it into the carbs) as you described. If you rebuilt your carbs yourself, you'll have replacements for those check valves in your rebuild kits (you'll have two check valves and two pegs per rebuild kit, so you should have 6 of each).

    Note: They were a NIGHTMARE for me to replace just because of how tight of a fit the pegs are. It takes patience and finesse to get them in place (two things which I apparently lack). You can take a look at my recent thread "wrong fuel pump check valves" to see some of the suggestions people gave on how to get them in place.

  7. #7

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    Awesome thank you. I found a place for a new fuel pump for $49. Thought this was a good deal so I picked it up.

  8. #8
    Quote Originally Posted by bryan428 View Post
    Awesome thank you. I found a place for a new fuel pump for $49. Thought this was a good deal so I picked it up.
    If your pump has never been rebuilt or anything you probably made a good decision. I ended up buying a new one as well (relatively new at least - it had really low hours). You'll have new diaphragms, new check valves, new gaskets, etc.

  9. #9
    old school big raider's Avatar
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    Quote Originally Posted by kingstretch View Post
    If you're talking about the diaphragm (the big plastic circle), I wouldn't really think the crease would have that much of an effect (as long as there isn't a tear) since it would still be able to move back and forth. If you're talking about the check valve (the small plastic circle), it could definitely cause an issue since it would allow fuel to travel in both directions through the pump.

    Edit: I fully expect that someone will argue with me about the diaphragm being creased, but it seems to me like it would still be able to "pump" even if it had a crease (although ideally of course you don't want it to be creased).
    diaphragm creased will definately have an effect-it will still pump but not fully-my first raider had this exact problem and would blubber on top end until i replaced clear plastic diaphragm

  10. #10

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    Great I'm hoping this helps in my case. My fuel pump just dangles freely off the carb rack, is this the normal setup, or should it be bolted or zip tied on somewhere?

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