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XJ750 Running fine but general issues.

Discussion in 'XJ Technical Chat' started by Maxwell Partridge, Jun 24, 2019.

  1. XJ550H

    XJ550H Well-Known Member Premium Member

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    2k rpm is when your carbs running off of the pilot jets.
     
    Last edited: Jul 23, 2019
  2. Maxwell Partridge

    Maxwell Partridge Member

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    So that indicated something wrong with the main jets? Should I just order a rebuild kit to rule out and issues?
     
  3. Maxwell Partridge

    Maxwell Partridge Member

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    I'm not trying to hide information, but some of the pilot jets are chewed to hell where the P.O. had tried to take them off using the incorrect size flathead and destroyed some of the brass, one of them I have to use locking pliers because it's so smoothed I cannot get it out otherwise, and most on the spare carb he gave me are like that too... But the primary jets looked fine, maybe ever so slightly showing signs of careless screwing.
     
  4. XJ550H

    XJ550H Well-Known Member Premium Member

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    your bike runs off of the pilot jet circuit to 2 to 3k rpm and that's when mains kick in.
     
  5. Maxwell Partridge

    Maxwell Partridge Member

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    Well so here is another update, the bike is actually running good now but rather quirky. When it is cold the bike will spot and sputter at 1-3k rpm but after 20 or so minutes of riding and getting it warmed up good it runs nearly perfectly, the sputtering goes almost completely away! It will ever so slightly do it every once in awhile. The newest thing that confuses me is that when riding out the rpm the bike stays high rpm between gears, but it will slowly drop while the bike continues to accelerate. It feels like the power keeps climbing but the rpm is dropping, almost like it is running very lean and then fuel starts flowing better after afew seconds.
     
  6. Door dude

    Door dude Active Member Premium Member

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    Im just wanting to know, you said you had the idle mix screws out 4 3/4 turns correct ? Im wondering are the idle mix screws are doing anything anymore, sounds to me that the hole is wide open?
     
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  7. XJ550H

    XJ550H Well-Known Member Premium Member

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    once bike is fully warmed up set the idle

    if you are out 5 turns it would be time to go up a size in the pilots.
    you may have a vacuum leak in the mixture screw threads.
    also if your jets are that mangled you could have a leak under the head of jet allowing fuel to be sucked up the threads of the jet

    so carbs aside for a second.

    what is the idle voltage output at battery? and up to 2k rpm?
     
    Last edited: Jul 24, 2019
  8. k-moe

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

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    Given the description, I'd just pull the carbs, tear them down for cleaning and replace the messed up jets and seals.
     
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  9. XJ550H

    XJ550H Well-Known Member Premium Member

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    after rereading the whole thread. I would agree with k-moe replace the jets with new ones due to mangled and value unknown.

    did you ever check the shim clearances? I see where it was suggested but you did not reply.

    lost spark in plug 1 then plugs swapped it all fixed itself. make sure your plug wire ends are clean and tight. something happened when you swapped plugs.

    after shims resync the carbs
     
  10. Maxwell Partridge

    Maxwell Partridge Member

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    Alright, thanks everyone. I have the next two days off so I'll have some more time to fiddle with it and I'll be able to get back after that. I'm just going to bite the bullet and buy the 50 dollar rebuild kit from eBay that comes with an assortment of replacement parts and different jet sizes. I'll check the shims and will make sure I'm getting voltage tomorrow or the following day. I really appreciate the help so far from everyone replying, I'm at work with no service at the moment so can't give too much info but here is a reply to the questions asked:

    1. Idle mixture screws are out 4 full revolutions from soft bottom, any more and it starts to run poorly, and less and it sputters worse.

    2. I'll check the voltage readout soon.

    3. I'm just going to buy the full rebuild kit, any suggestions or should I just get the eBay one?

    4. Will check shims soon.

    Thanks again!
     
  11. Chitwood

    Chitwood Well-Known Member

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    That ebay kit isnt going to contain the most vital parts of the carb rebuild that you need. Yes it will have some jets in it and a few other things but you really need throttle shaft seals and fuel tube o rings. Yes you still need jets, needles, seats, bowl gaskets, etc but there much more to doing the job properly than just a few jets. When we suggest doing an in the church of clean overhaul you have to read the thread and follow it religiously. I have been through 3 sets of carbs on 3 bikes and I can tell you that the first set took the longest and had to come off again to make right what I didnt get right the first time. By the 3rd set they turned out pretty freakin nice. Minus the fact that I tried to use o rings instead of actual throttle shaft seals which did lead to them being pulled again for replacement of those. However, if I had taken my own advice and replaced those with the proper seals the first time I would have had no issues and the bike is running great. Just my 2 cents. And while you have the carbs off, broken apart into 4 separate bodies, soaking in carb dip, that's the most convenient time to pull the valve cover to measure and correct valve clearances
     
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  12. Timbox

    Timbox Well-Known Member

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    +1 on the ebay stuff, normally those kits are underwhelming to day the least! When it comes to the carbs spend the $$ and get the good stuff. IMHO
     
  13. k-moe

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

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    The Ebay kit will have an abundance of parts that will not fit correctly.
     
  14. Maxwell Partridge

    Maxwell Partridge Member

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    Alright! I'll go to the thread for the taking carb to church and follow it.
     
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  15. Chitwood

    Chitwood Well-Known Member

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    Dont mean to sound like I'm on a soap box but even I didnt really get it until I had done it. Wasn't very long until I realized exactly what the other more knowledgeable members were getting at. Do it right the first time and be done with it for quite some time. Granted there's room for error in most things but due diligence pays off.
     
  16. Maxwell Partridge

    Maxwell Partridge Member

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    I have been swamped as usual but I decided to take some pictures to show you guys what I'm dealing with. First two are of the spare carb I have I'm using for parts, the condition of those pilot jets are near identical of the same inside the carb currently minus the really destroyed one on the left end. And the jet in my finger is the 110 main jet which I had 4 of installed before taking the 4 120 jets from the spare and swapping them in.
     
  17. Maxwell Partridge

    Maxwell Partridge Member

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