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Help Needed! RPM Jumps or Revs...Carbs?

Discussion in 'XJ Technical Chat' started by lpayne, Jul 9, 2008.

  1. lpayne

    lpayne New Member

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    I just recently bought a 1981 XJ650 that had been stored in a barn for about a year or so. Initially it ran fine but had power issues. Had no pep and wouldn't reach much over 50mph. I figured that since it had been setting for awhile that the gas was old. So I rinsed the tank and added carb cleaner to the new gas. Now the RPM will jump while holding steady going down the road. At times it will reduce itself only to do it again. When I come to a stop it may idle down only to jump to over 7000RPM in a flash. The only thing to do is kill it. When I restart, it may stay at idle for a few seconds, but then start rising again. I figure the carbs need to be pulled because a float or needle is sticking. Can anyone help with this problem. I need to get things fixed asap. Its now my only transportation for the next few weeks.
     
  2. RickCoMatic

    RickCoMatic Well-Known Member

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    It sounds like you are going to have to pull the rack of carbs and do a thorough cleaning.

    I can's see how you can get around that with the bike behaving like it is.
    You'll have to clean the Jets and Passages and scrub the Diaphragm Piston Bores.

    Clean Carbs are necessary to have a well running bike.
     
  3. yamyboy

    yamyboy Member

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    The best thing to do is pull the carbs and pull them apart and clean and rebuild the and set the mixture idle back to stock. Carb cleaner in the gas is a preventitive thing not a fix , it wont get all over to clean it . You need to soak it and do it right the first time . Take your time read all you can cause the set up is tricky but can be done . When these things are toned right thay run GREAT and will not let you down but keep on top of things.
     
  4. lpayne

    lpayne New Member

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    Thanks Guys! I figured I would end up pulling the carbs and giving then a good cleaning. Now tell me the best way to get them off the bike.
     
  5. RickCoMatic

    RickCoMatic Well-Known Member

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    Undo the clamps.
    Push the Airbox boots back into the airbox.
    That gives you enough room to operate and take them out of the Manifolds without disturbing the Manifolds (risky).

    The hard work is getting them off and back on.
    The rewarding part is they'll get cleaned and the bike will run right.
     
  6. lpayne

    lpayne New Member

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    Thanks for the info! I'm sure over the next couple weeks this forum will be my most visited website.
     
  7. lpayne

    lpayne New Member

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    OK, The carbs have been torn down, soaked, blown-out, brushed, poke-out, sprayed-out, soaked again, sprayed-out and then put back together with new kits. However, I am still haveing the surges in RPM up to 7K, especially in first gear and neutral. Otherwise, the XJ650 is moving around much better as long as I don't have to stop. Any ideas?
     
  8. stereomind

    stereomind Active Member

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    didja check for vacuum leaks all around the carb boots? Has the bike been synced recently? or at all?
     
  9. RickCoMatic

    RickCoMatic Well-Known Member

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    The surges mean that you are getting both Fuel and Air into the Chambers.

    You need to look for an air leak.
    The Carbs probably need to be vacuum synced
    The Main Jet Fuel to sustain 7K rpm's is Main Jet supplied.
    Look for sticking Diaphragm Pistons allowing Main Jet Fuel in.

    Look for anything that might pull the Throttle Cable opening the Throttles
    Tight Cable

    Things that are going to open the throttles
    Allow air in
    Allow Main Jet Fuel in.

    7,000 rpm's is way up there.
    The throttles have to be opened some to get that.
     

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