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I'm getting too old for this--maybe

Discussion in 'XJ Technical Chat' started by tabaka45, Jun 9, 2020.

  1. tabaka45

    tabaka45 Well-Known Member

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    My XJ700n has been running perfectly for the last several months. But today it cut off for not apparent reason. It would crank over but not fire off. If I waited a few minute it would act like it was starting but wouldn't. It acted like it had no gas, but the tank was about 1/2 full. Finally I call the wife and she picked me up so that I could get the trailer to get it home. That took about 30 minutes. Sure enough it fired right up and ran for about 30-45 seconds and died. So, it appears to me that I have a sudden fuel problem. I'm interested in suggestions on trouble shooting this before removing the carbs. They are clean and I run a good inline fuel filter. Setting he petcock to prime did not solve the problem.
     
  2. Polock

    Polock Well-Known Member

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    take the fuel line off, see if reserve works then
     
  3. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Fuel cap vent may have become plugged, resulting in a "fluid lock" in the tank..........pop the cap open next time this happens, see if you hear a "whoosh" and can then start it again. Also, make sure there no upward rise/ramp in the fuel line, a vapor bubble can form in such a spot.
     
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  4. Minimutly

    Minimutly Well-Known Member

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    I would have thought, given he said that there was half a tank of fuel in there, he would have allready done that? Isn't it the first thing everyone does?
     
  5. Franz

    Franz Well-Known Member

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    Do you have an auxiliary tank you would use to supply fuel to balance the carburettors? Try that to see if it runs without cutting out.
     
    Last edited: Jun 10, 2020
  6. Franz

    Franz Well-Known Member

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    My father told me that when I was young. He opened the fuel cap on my MZ and the bike started. It was no head turned that old two stroke but it got me to work and then I wanted another bike. Had a cup on the underside of the filler cap to measure the two stroke oil.
     
  7. Rusty81

    Rusty81 Member

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    Is the filter on the Petcock There?
    My 700 did the same to the PO. He was using a different tank without a filter and the carb fuel lines were plugged solid with rust.
     
  8. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    Yep, first thing to check is that you can verify that fuel is flowing
     
  9. Jetfixer

    Jetfixer Well-Known Member

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    Another thing to check is to replace the fuel line from petcock to carbs ...it is possible it can collapse inside line.
     
  10. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    That would be part of verifying fuel is flowing
     
  11. tabaka45

    tabaka45 Well-Known Member

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    Thanks. The first thing I did was open the fuel cap and that didn't help. Tomorrow I will start the process, and I'm sure hoping it is somewhere in the fuel line or at most the petcock. I'll let you know.
     
  12. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    Here’s what I find is the easiest way to determine fuel flow to the carbs......
    1. Pull the fuel line off of the carb fuel “T”
    2.turn the petcock to PRI.......fuel should freely flow. If it doesn’t, or just dribbles, open the cap. If it now flows, your cap valve is stuck. If it still doesn’t, you have to work your way back up up the line
    3.if it Flows freely on PRI, switch to RUN or RES and turn the key on and press the starter button. The vacuum should open the petcock diaphragm and fuel should flow. If it does, the issue is in your carbs. If it doesn’t the issue is with the petcock, vacuum line, or tank
     
  13. Polock

    Polock Well-Known Member

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    that could be a heat problem, looked at the valves lately?
     
  14. tabaka45

    tabaka45 Well-Known Member

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    Finally got around to trouble shooting the problem today. Here is what I have found.

    Battery, 12.87 volts, 12.75 v at idle, 13.8 v at 3000 rpm
    All plugs firing and look very good--nice light gray color
    Disconnected petcock from fuel line--it pours gas at Prime and at both Run and Reserve (with engine running)
    Fuel filter is clear and gas pours through it
    No water in the fuel
    Ran the carbs dry and set the petcock to Prime. All carbs filled and would flow gas from the nipple when the bowl screw was opened.
    Checked the sync and the carbs are in sync
    Valves were adjusted within the last 4000 miles and I have a nice ticking sound.
    Right now the bike starts, idles and seems to run perfectly in the garage

    The only thing I see that seems odd to me is that there is always air in the fuel line between the petcock and the filter but fuel can be seen passing through it. My filter is located midway between the fuel T on the carbs and the petcock and is not quite vertical. I have everything positioned so that there is a constant upward slope in the fuel line so I am somewhat curious as to why the bubble would not pass up and through the petcock, especially at Prime. (Interestingly, the same thing happens on my Honda Rebel, but it has never caused a problem, and I've been told that it is fairly common.)

    Before this happened I was confident that I could take the bike anywhere anytime. That confidence has been shaken. Not excited about taking the carbs off . Could there be some electrical (I hate electrical) issue that would cause this?
     
  15. Polock

    Polock Well-Known Member

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    when it quit, did it quit like key off or did it sputter out and die slowly?
    would it start right now
     
  16. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    That makes it sound more like the relay issue I had with my 900 a number of years back—-sudden quit, dead as a doornail.... trailered home—- found nothing, three days later while just standing next to the bike I heard a single faint relay click. I touched the start button and it fired right up.... never happened again
     
  17. tabaka45

    tabaka45 Well-Known Member

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    When it left me on the side of the road I was coasting to a stop sign and it cut off. Let the clutch out to try and jump start it but it would not. Coasted to a stop and it cranked over very well but sounded like it was getting no fuel. Got the trailer--about 30 minutes-- and it fired right up and ran for about 30 seconds and shut down and would not restart. A couple of days later I hit the starter and it fired right up. It shut down after about a minute, but it has often been a little fussy until it warms up and reaches normal idle --about 12-1300. Right now it starts easily and seems to run perfectly.

    What relay would I be looking for and where. Electrical is not my strong suit.
     
  18. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    I don’t know, cuz when mine did it, it was dead. Wouldn’t turn over. Wouldn’t do anything even with a jumper battery.......absolutely nothing, til a few days later and I hear that tiny click somewhere.
     
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  19. JohnStonePhoto

    JohnStonePhoto Member

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    Be sure to check your coils and the TCI, they'll both break down with heat and then work again when they're cold.
     
  20. tabaka45

    tabaka45 Well-Known Member

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    I have ohm'ed out the coils but I will look at them again. Have no idea how to check the TCI, and in fact I'm not sure I even know where it is. Like I say, electrical is my strong suit.
     

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