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Jetting woes

Discussion in 'XJ Technical Chat' started by Jake750, Oct 14, 2021.

  1. Jake750

    Jake750 Member

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    1986 Radian 600.

    So just got my carbs back from being professionally rebuilt. Hooked them up, fired it up, checked for vacuum leaks, synced them and called it a day. The bike was idling well so I assumed all was well. I got on the highway and realized that I my top speed was about 65mph in 6th. The bike pulls strong up until about 7000 rpm's. After that it just refuses to accelerate.

    On my way back home the idle was out of wack. after reving it would hang around 3500 rpm before returning to under 2000. The idle was also slowly increasing as the engine got hotter.

    I assumed I had a vacuum leak that was causing it to run super lean. I checked for leaks by using an unlit propane torch with the bike idling and watched for a bump in rpms. No vacuum leak as far as I can tell.

    The PO installed aftermarket jets of unknown variety, im pretty sure theyre one of the ones that come in that dynajet stage 1-3 kit. The PO also installed those aftermarket adjustable needles. The person who rebuilt my carbs said that he replaced the main jets with oem ones but left the needles in the position they were in when he received them which was the needle on the highest setting (the needle goes as far down into the jet as it can). The bike ran kinda shitty before I sent in the carbs, but now it runs super shitty.

    My best guess is that it is either running super lean or super rich. I have a feeling its running lean. The bike starts up right away and idles decently so I'm assuming there's just something going on with the main jet. Any advice would be appreciated.

    Thanks in advance.
     
  2. XJ550H

    XJ550H Well-Known Member Premium Member

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    did you check the wet set fuel levels? may be low and you are running out of fuel at higher rpm.

    you can use wd 40 to check for leaks it will seal the leak as it is sucked in and cause rpm change.
    starter fluid will work too but cause a jump in idle and is more flamable keep a fire extingusher handy
     
  3. Jake750

    Jake750 Member

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    Would an aftermarket non-vacuum style petcock possibly be causing fuel starvation?
     
  4. Minimutly

    Minimutly Well-Known Member

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    Fuel starvation from too low a float setting will feel different to starvation from the petcock.
    Starvation from the floats is there all the time, the latter comes in and hits you like a brick - one minute pulling like a train, the next, nothing, engine dies a death. That’s my experience anyway.
     
  5. Jake750

    Jake750 Member

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    I can rule out starvation from petcock then.

    If it helps, there is also a decent amount of smoke coming from the exhaust.
     
  6. k-moe

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

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    WD-40 won't seal the leak. It will add extra combustables to the mix.
     
  7. Minimutly

    Minimutly Well-Known Member

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    “Professionally rebuilt” - I cringe at the sight of this term, however, I will make a suggestion that you won’t like - send them to @hogfiddles - if he’ll do them - that way I believe you can be sure they are correct. Sure it will mean paying twice, but unless you know, or have the inclination to go through them yourself, this is the best way.
     
  8. Jake750

    Jake750 Member

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    Minimutly, it was through wiredgeorge. A friend recommended them to me. If I had know about hogfiddles I would have done that. I already shipped my carbs when someone mentioned Hog does rebuilds. They're not Hogfiddles but they know what they're doing.
     
  9. Minimutly

    Minimutly Well-Known Member

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    The po installed main jets were fine with aftermarket needles - the aftermarket needles are not fine with Oem jets. That’s how I see it.
    I’ve only rebuilt 3 racks, and each one worked well enough right from first refitting to ride the bike - so why didn’t your rebuilders efforts?
    If your bike is original, get some original needles fitted, and hope the jets used by the rebuilder, and everything else he did was correct.
    If you want to persevere with the aftermarket needles clean the plugs, take the bike for a few mile spin at constant speed, just below where it fails to accelerate any further. Then hit the kill switch, clutch in and park up. When the engine cools enough check your plugs. White = weak, black = rich. Move the needles down if rich, up if weak. Fingers crossed the needles profiles are similar to oem - your pistons might thank you.
     
  10. Jake750

    Jake750 Member

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    I mailed them to the rebuilder. They didnt have an opportunity to test out the bike or anything.

    Is that a thing that aftermarket needles are not compatible with oem jets? or is that just a hunch? My hatred for the tedious process of reinstalling the carbs burns brighter than the sun. The fewer amount of times I have to remove and install, the better.
     
  11. Minimutly

    Minimutly Well-Known Member

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    See my suggestion above ^ The good thing is, you can remove carb tops without removing carbs, once the tank is off - ooo, or am I thinking of my vmax??
     
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  12. Jake750

    Jake750 Member

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    Anyone know if its actually possible to work on the top part of the carbs without removing them?? I feel like you'd have to have some sort of bendy screw driver and hands like a surgeon for that to work.
     
  13. Jeff Witt

    Jeff Witt New Member

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    Jake750,

    I was able to pull the needles out from the top of all 4 carbs on my XJ650 after pulling the tank. You may need to do a little screwdriver magic with a steady hand but it is a lot easier than pulling the carbs out again.

    Jeff
     
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  14. Jetfixer

    Jetfixer Well-Known Member

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    A couple of items , have you checked your valve clearance yet ? Done a compression check ? Were carbs only bench synched or have you done a running synch? These can effect the running of the bike , I have rebuilt several carbs, a set I had once would run fine at idle , when you put it under load felt like it was running on three cylinders, I had a diaphragm that was not going all the way up once I corrected that no more problems ...try the "clunck" test , through back of the carb with your finger push slide all the way up and drop it should move smoothly if you have resistance that is where to look .
     
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  15. Jake750

    Jake750 Member

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    Jeff thank you. I've been procrastinating due to my hatred of reinstalling the carbs.

    Jet, I've done all of the usual jazz when buying a used bike from the 80's.
     

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