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Fuel blowing out of throttle shaft!!!

Discussion in 'XJ Technical Chat' started by mdsymonds, Apr 12, 2006.

  1. mdsymonds

    mdsymonds New Member

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    Hi all
    I have been reading this forum non-stop for the last few day(ok not non-stop).
    Now I have a question of my own.
    I have just got myself a 1983 xj750 jap import so basically a xj900 with a 750 engine.
    I noticed that fuel is blowing out of my throttle shafts and I get lots of popping noises and backfiring.
    First question:
    1. Should'nt air be sucked into the leaky shafts, not air blowing out?
    2. Anyone know where to buy new throttle seals in the UK?
    3. Do I need to check the valve clearances?
    Thank
    Malcolm
     
    mdsymonds, Apr 12, 2006
    #1
  2. Robert

    Robert Active Member

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    A complete tune up (done by yourself of course, not the local mechanic, you won't learn anything that way) is a good start and the valve clearances would be a capitol idea. Just be sure to have a new valve cover gasket on hand before you begin (unless of course you have replaced it recently). I cannot attest to the shaft vaccum/pressure issue but I would tend to believe there should indeed be a vaccum (they bisect a venturi right?). Worst case, contact one of our brothers here on the forum to have them send you some seals from here in the colonies. Any other thoughts gang? Let's help this poor fellow out!
     
    Robert, Apr 12, 2006
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  3. jdrich48

    jdrich48 Member

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    Last edited by a moderator: Oct 25, 2014
    jdrich48, Apr 12, 2006
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  4. BlueMaxim

    BlueMaxim Active Member

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    Fuel flows via gravity through the fuel line and into the fuel passages then to the float valves to fill the float bowls, once the float bowls are full the float valves close off the fuel flow. This eliminates the vacuum created by the venturi in the carb throats until the floats sink down and refill the bowls. So during the cycles you will have a time of no vacuum. Fuel will leak out then and maybe during the filling of the bowls because the draw on the fuel passages will be small compared to it's effect on the emulsion tubes and jets. Remember the fuel pressure has to be greater than the fuel flow or you will have "insufficent fuel" flow.
     
    BlueMaxim, Apr 13, 2006
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