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1982 XJ750 Maxim Redline at startup

Discussion in 'XJ Technical Chat' started by Winsleydale, Mar 18, 2019.

  1. Winsleydale

    Winsleydale New Member

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    Hi everybody,

    I joined the forum to see if I could get some pointers on an issue I am having. I picked up this bike as a trade for an old pickup with a blown transmission. It's got some problems (Leaky Chinesium petcock is awaiting proper replacement, tach doesn't move, blinkers light up solid) but the biggest one for me right now is that as soon as I start the thing up, it screams at me like a drunken sailor until I shut it off.

    I had originally pulled the carbs to make sure nothing was sticking as I had problems with it stalling in idle before, but I didn't take the carbs apart or mess with them at all, other than to move the slides up and down to make sure they were moving freely (they all were). The butterflies checked out okay to my untrained eye - no big gaps or anything, throttle shaft turns freely and snaps back.

    Two of the 4 vacuum nipples on the intakes were uncovered when I got the bike. I understand that one was attached originally to a line for the OE vacuum petcock which I will be replacing, the other was just open. In the interest of sealing vacuum leaks, I have capped all four for now.

    I have noticed that my throttle doesn't want to move very far or move smoothly, so I would think that the most obvious explanation is a stuck-open throttle - but like I mentioned, I didn't mess with anything and it didn't do this before, and from fiddling with the shaft linkage I am reasonably certain that it's snapping shut properly.

    I am not a mechanic, however, and obviously something is still very wrong. I figure I'm going to have to pull the carbs back out but what the heck am I even looking for at this point?
     
    Last edited: Mar 18, 2019
  2. Chitwood

    Chitwood Well-Known Member

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    I would suspect a vacuum leak. Throttle shaft seals will cause a leak, cracked intake boots, bad intake boot gaskets where they meet the cylinder head, etc. I would also make sure the caps you installed on the intake boots are sealing properly even if they are only temporary as this will cause a massive vacuum leak that could explain your symptom
     
  3. Ryengoth

    Ryengoth Active Member

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    I would pop the tops and check all of the diaphragms for pin holes as well as what Chitwood suggested. If the slides don't drop down with a thud when you pick them up and release them then bores and slides need a polish.
     
  4. Winsleydale

    Winsleydale New Member

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    I'll pull the carburetors again as soon as I get a chance. Thanks for the tips.
     
  5. XJ550H

    XJ550H Well-Known Member Premium Member

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    start by lubing the throttle cable to eliminate it as a problem
    check to see if idle screw in rear of carbs is turned in to far.

    then check that the throttle end is properly seated in the holder on the carbs,
    and check that the throttle cable is properly adjusted should be a little play or slack in the throttle grip and where it connects to throttle shaft.

    also check to see of the carb linkage is hung up on the head

    and routed
     
  6. raskal

    raskal Active Member

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    what is recommended for cable lube? I know cable lube sprays cans exist, but are they required, or is a dry graphite enough?
     
  7. Ryengoth

    Ryengoth Active Member

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    I use Motion Pro lube with the cable oiler tool they make. Works great.
     
  8. Rooster53

    Rooster53 Well-Known Member Premium Member

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    Also make sure you did not reverse the choke and throttle cable - it would not be the first time this had been done.
     
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  9. Winsleydale

    Winsleydale New Member

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    Hey guys, just finally had a chance to get back to the bike.

    I took the lids off each carb and checked for holes in the diaphragm. I found none, and each slide returned smoothly with a light *dink* when I pulled them up to check freedom of movement.

    I made sure my cables were in the correct places, and that they weren't hanging up in their sleeves.

    I also started the bike with one spark plug disconnected, starting in cylinder 1 and moving down the line, to try and isolate a problem carb, but they all wanted to run away on me.

    Throttle is now turning nicely but I am not sure where to look next.

    Edit: I'm a dummy. I still haven't backed off the idle screw... I'll try that next.
     
    Last edited: Mar 21, 2019
  10. Winsleydale

    Winsleydale New Member

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    The bike ran when I got it and there weren't any caps at all, just open vacuum ports. Granted it stalled constantly, but it never did this.
     
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  11. Winsleydale

    Winsleydale New Member

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    So here's a late update since I forgot to post. My throttle was not stuck open but when I reinstalled my carbs, one of the hose clamps got in the way and held it partially open.

    A stupid mistake, but when you just can't get it right, it's almost always something stupid...

    The bike runs great now and has been a lot of fun!
     
    Plug and k-moe like this.
  12. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    The best mistakes are the ones that are easy to fix. :)
     

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