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10 miles, fuel fouled plugs, over and over....82 xj seca

Discussion in 'XJ Technical Chat' started by jsthunter, Mar 17, 2008.

  1. jsthunter

    jsthunter New Member

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    I have a 82 750xj that is about to get the boot !! I have tried just about everything to get this bike to stop fuel fouling the plugs without luck. I spent 400.00 to have the carbs synched and a new petcock installed, still goes 10 miles starts cutting out, then dies all together. the plugs are black and dusty...then, change the plugs and off it goes again just fine...NGK , Autolite, it dont matter.....for about 10 miles. Damn, this makes me feel dumb, but this bike is kicking my a$$. Could the cylinder head need a rebuild? (vacuum leak) , iginition pac? any insight appreciated.

    JJ
     
    jsthunter, Mar 17, 2008
    #1
  2. xj750_Pete

    xj750_Pete Member

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    How does the bike run for those 10 miles or less? Easy start? Stumble upon acceleration? Smoke coming out of the exhaust? How many miles are on it? Without clues it can be anything.
    For spark plug fouling it could be:
    clogged air filter
    stuck choke
    incorrect spark plug range
    incorrect spark plug gap
    incorrect main jet
    incorrect needle jet position
    burnt out ignition wires
    burnt out ignition coil
    weak alternator/worn alternator brushes
    valve stem seals worn
    cracked head gasket
    worn piston rings
     
    xj750_Pete, Mar 17, 2008
    #2
  3. TIMEtoRIDE

    TIMEtoRIDE Active Member

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    Count and record the #'s of turns of the 4 idle mix screws. Maybe the guy who messed with the carbs set them way out. Try 2 1/2 turns. And remove your air filter for a test run.

    I was also thinking your bike would run perfect on a 50-50 mix of alcohol !
     
    TIMEtoRIDE, Mar 17, 2008
    #3
  4. ArizonaSteve

    ArizonaSteve Member

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    You didn't say what speed you are going when it fouls the plugs but if you are driving slow and it fouls the plugs the pilot jets are too large, if you are going medium speeds at part throttle and it fouls the plugs the tapered needle is set too high (maybe some idiot put washers under it?) and it you are driving at full throttle and it fouls the plugs the main jet is too large. If it does that at any speed the float level is too high or the needle valves are leaking.
    Take the carbs apart and put the jets all back to stock sizes and make sure the tapered needles fit properly and are going all the way down and the floats are set to the right level (fuel at the top of the bowl) and the needle valves are not worn our and leaking.
    BTW, you'll need to get a service manual and follow it to do all that.
     
    ArizonaSteve, Mar 17, 2008
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