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Idle return... FIXED

Discussion in 'XJ Technical Chat' started by 2dawson, Jul 28, 2009.

  1. 2dawson

    2dawson Member

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    I decided to try to sync my carbs to cure a mild problem of idle hanging at 2000 rpm for a few seconds before returning to idle. I can find no vacuum leaks with propane or carb cleaner. The slides fall very wuickly and smoothly with the prescribed "clunk".

    I built a 4 tube sync tool from the info from another site using 2 stroke oil for the fluid. My problem is when they are connected and I start the bike, it immediately tries to suck all the fluid into number one cylinder adn of course the level on the other 3 fill with bubbles. I can stop the engine before the oil gets to the carb. I tried to sync with a single vacuum gauge and think 1&2 are close together but it takes so long that I didn't get 3&4 together.

    I guess my question is how do I avoid sucking all the oil to #1 while syncing? I've never done this before so any help is appreciated.

    Jim
     
    2dawson, Jul 28, 2009
    #1
  2. MiCarl

    MiCarl Active Member

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    Re: Idle return...

    I assume all 4 tubes connect together - below the oil level.

    The oil is getting sucked into one cylinder because they are out of sync. The one sucking the oil has lower pressure - it's butterfly is too far closed relative to the others.

    How full is your manometer? It should probably be filled to about 1/4 it's working height.

    Only way to guarantee it won't suck the oil is to make it very tall - 20 feet or more. That's the reason old fashioned carb sticks used mercury. Perfect vacuum will only pull 29" or so of mercury.
     
    MiCarl, Jul 28, 2009
    #2
  3. 2dawson

    2dawson Member

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    Re: Idle return...

    The tubes are 48" tall, filled to about 18". I sure can't make one 20' tall. :)

    I guess I'll give up on this project and try some other way, Oh, well, another $20 in the trash.
     
    2dawson, Jul 28, 2009
    #3
  4. MiCarl

    MiCarl Active Member

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    Re: Idle return...

    You'd get a bit more usable range if you had the initial level at 12".
     
    MiCarl, Jul 28, 2009
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  5. helmet

    helmet Member

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    Re: Idle return...

    if you are worried that #1 is that far off, you may want to pull them and bench sync the carbs. after you get them pretty close, fire it up and sync on the bike.
     
    helmet, Jul 28, 2009
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  6. 2dawson

    2dawson Member

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    Re: Idle return...

    I'm trying everything I can to avoid pulling the carbs again, but I guess I'll have to.

    Thanks,
    Jim
     
    2dawson, Jul 28, 2009
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  7. MiCarl

    MiCarl Active Member

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    Re: Idle return...

    I just pulled out the fingerz and toez and did some math. 1psi ~ 30" of oil. In other words, you don't have to be off by much to suck the oil out. Bench syncing won't even get you close.
     
    MiCarl, Jul 28, 2009
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  8. 2dawson

    2dawson Member

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    Re: Idle return...

    Then how are others using a similar tool and syncing the carbs? Do I need to buy three more vacuum gauges?

    Jim
     
    2dawson, Jul 28, 2009
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  9. helmet

    helmet Member

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    Re: Idle return...

    but if the butterfly is closed completely it will pull hard through any available point of entry and suck the oil in. I think the bench sync will make a difference. mine would barely start and I pulled the carbs to bench sync and it fired right up when I was done. they didnt look too far off in the light. but they were all a little off from 3. I used a high performance feeler gauge (a trash bag tie with the paper torn off) and synced them that way. worked great.
     
    helmet, Jul 28, 2009
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  10. 2dawson

    2dawson Member

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    Re: Idle return...

    I think I have one of those feeler gauges around here somewhere, I'll give it a try. :)

    Thanks,
    Jim
     
    2dawson, Jul 28, 2009
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  11. 2dawson

    2dawson Member

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    I tried again to sync the carbs with Rick's "Old school" method. This time it worked like a champ. I guess I just wasn't patient enough the first time I tried it.

    Idle now returns to 1100 immediately like it should.

    My frustration level has subsided once again.

    Thanks to everyone for their help.
    Jim
     
    2dawson, Jul 29, 2009
    #11

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