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Carb fun continued

Discussion in 'XJ Technical Chat' started by mcdermap, Apr 17, 2016.

  1. mcdermap

    mcdermap Member

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    Hey guys, just got back from seasonal work in the great white north. Hoping to get my ol' 82 xj750 seca running decently this time around.

    Bike starts and runs fine. As soon as she's warm and I hit the throttle, my idle gets stuck at 3-4k until I press down on the center balancing screw.

    So, valves are in check, carbs are cleaned out, but with old internals, got a bench balance, and began to synch until she started revving high. Mistakenly ordered a carb kit for an 11M, received three jets (43, 112, 122,) bowl gasket, needle, needle jet, float needle, float valve, etc.

    Planning to pull carbs and replace float needle from the M11 kit tomorrow. Big question, should I change any of the jets? Or the main needle? Only the pilot matches the M11 specs from info overload hour. Feeling a little timid as I'm uncertain of how changing float needle will affect carb tune and would rather not pull the carbs for a fourth time.

    Thanks in advance.
     
    Last edited: Apr 17, 2016
  2. tabaka45

    tabaka45 Well-Known Member

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    If your bike has stock air filter and exhaust system then the only reason to change any of the jets would be if a they are not the stock size or if you determine that they have been drilled at some earlier time. It's much easier to get a stock bike running well than to try and get a modified bike running well. As to your idle issue have you simply tried to lower the idle with the idle screw? If so, are you absolutely sure the enrichment circuit is fully closed?
     
  3. rocs82650

    rocs82650 Well-Known Member

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    What he ^ said.

    Gary H.
     
  4. mcdermap

    mcdermap Member

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    Hey Tabaka,
    Yes, stock exhaust and air intake. In fact, just replaced carb boots. Idle screw is all the way out, and enrichment is infact closed up.
     
  5. mcdermap

    mcdermap Member

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    Thanks Gary & Tabaka, will keep jets the same and change just float needle.
     
  6. tabaka45

    tabaka45 Well-Known Member

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    Then I would next suspect a vacuum leak or excess fuel from somewhere.

    When you start it do you have to use the enrichment circuit? Does it then idle well--1000 rpm approx- without the enrichment? If so, does it eventually increase the rpm to 3-4k on its own? What I'm getting at is that my bike--when starting cold-- idles very low without the enrichment circuit on. As it warms up with the enrichment on the rpms increase and will finally go to approx 4k if I leave it on, which I don't. Warm and without enrichment it idles at 1100. Therefore, if your bike --cold--starts and idles well without enrichment it would indicate that extra gas is being picked up, either through a leaking enrichment plunger, much too rich pilot system, very high fuel level, or somewhere else, including a vacuum leak.
     
  7. mcdermap

    mcdermap Member

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    Yep- about spot on tabaka. I need choke/enrichment to start, then when warm-ish, she'll idle just fine without choke at 1100-1200 with idle adjust backed all the way off. She'll then idle up to 4k or hover at 4k if I nudge the throttle at carb body, and stick there until I press down on the center balancing screw (brings her back down to 1100-1200.)

    Just pulled the carbs, and about to replace float needles and valves, which were a little worn, then will check throttle shaft o rings and see if that does it.

    I guess next step from there (assuming reassembly, wet set, and still hanging idle) is check for leaks with carb cleaner?
     
  8. tabaka45

    tabaka45 Well-Known Member

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    While you have them off do a really good bench synch and be sure the throttle plates aren't open too much and that all are equal. If they are open too much or if one is way off you could get the results you are having. You may find this is the problem. You should not have to have the idle adjustment screw all the way out.
     
  9. XJ550H

    XJ550H Well-Known Member Premium Member

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    your needle valve may be 1mm longer or shorter than what you have now measure them it will affect your wet set fuel level.
     
  10. tabaka45

    tabaka45 Well-Known Member

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    By the way, when you re-do the bench sync, make sure to set the idle screw in the middle so that you will have adjustment in both directions.
     
  11. Jetfixer

    Jetfixer Well-Known Member

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    Check the butterflys if they are not centered this can cause your problem there are 2 small screws on the shaft loosen them the plate will move a small amount , tighten back down see if you can see light round plate . ( hold up to a light source) ( tighten screws , but remove one at a time put a drop of blue lock tight on threads and reinstall) You have something holding butterflys open. Or what tabka45 said ;) Why your at it go to the Church of clean go to xj4ever catalog order new shaft seals if you have not replaced yet. Saves a lot of head ache later.
     
  12. Polock

    Polock Well-Known Member

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    1200 then blip goes to 4k.
    Your running on 3cylinders the blip starts the fourth going.
    Cant bring it down with the idle knob but Pushing on the sync screw does, says your not synced yet.
     
  13. mcdermap

    mcdermap Member

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    Hey there guys, quick update. Did throttle shaft seals the cheap n' dirty way (o rings and some RTV,) replaced float valves and needles, reset float levels (plus or minus 1mm from 3mm from top of float bowl.) Did a bench synch, had a particularly hard time getting her started, and now she's sitting at 6k w/ idle adjust backed out, throttle disconnected and choke shut.

    Guess I'm doing a shit job of bench synch based on above suggestions, will re-read some stuff and try again tomorrow.

    Thanks for the suggestion jetfixer, but don't have time for Len presently due to unpredictable contract work.

    Polock, will also run up to 4k when she's hot. Haven't had opportunity to finish her running synch yet- looking more and more like it might not happen. Are you thinking it'it's dieseling at that point? So maybe check out coils & wires.
     
  14. mcdermap

    mcdermap Member

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    Edit- will be pulling RTV ghetto throttle shaft seals & replacing with old, given new crazy idle.
     
  15. mcdermap

    mcdermap Member

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    Thanks for the support guys! Got the old throttle shaft seals in, and did another few bench synchs. After reading a comment in a similar thread (mrdawson'$ carb tune issue)- the gist of which was get the fore hole half way covered while bench synching, I got her to idle satisfacorily. She's a runner and a driver now!

    Coming this fall: fork seals.

    Thanks again guys!
     
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  16. mrdawson

    mrdawson Active Member

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    glad to see that massive thread helped more than just myself.
     
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  17. PilotSmack

    PilotSmack Active Member

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    Proof that you just can't half-ass anything with these bikes.... lol RTV and O-rings
     
  18. Polock

    Polock Well-Known Member

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    Hay now, I use O-rings on the throttle shaft seals. But i'm a professional half-asser :)
     
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  19. k-moe

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

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    But that particular method of half-assery does do the job.
     
  20. rocs82650

    rocs82650 Well-Known Member

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    Hilarious :).

    Gary H.
     

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