Dialing the carb in for 9000'
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Thread: Dialing the carb in for 9000'

  1. #1
    Junior Member DicktheNick's Avatar
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    Dialing the carb in for 9000'

    So I changed the main jet to a 122 and adjusted the idle air screw to 2 turns out. Bike runs decent except for stumbling off of idle. I can leave the choke on and it cures that, but then runs crappy till I push the choke in. One thread I read talked about changing the pilot jet, which I've done on my 70s bikes, going leaner. Would this fix my idle stumble? Don't really want to drill holes in the airbox, but might look at the TPI valve I saw in another thread. Also not too interested in swapping the carb to a Chinese knockoff, at least not while the bloody bike's brand new.

    What say you?
    Dick in the Aspens
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  2. #2
    Senior Member Donzo's Avatar
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    If your looking for more air the TPI valve is great. I have it wide open at 7000ft and above. Half open for my local riding of 3000 - 7000ft and closed when at sea level to 3000ft. Closes tight, slick design. You may want to try 1 1/2 turns out as well if you are riding at 9000ft regularly. Good luck with getting it optimal!
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  3. #3
    Senior Member old w/??'s Avatar
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    Quote Originally Posted by DicktheNick View Post
    Bike runs decent except for stumbling off of idle. I can leave the choke on and it cures that, but then runs crappy till I push the choke in.
    One thread I read talked about changing the pilot jet, which I've done on my 70s bikes, going leaner.

    Are you asking if you should go leaner on the pilot jet - or just saying in the 70s you've changed those jets going leaner?
    Not a mechanic; but you said leaving the choke "on" (making it a more gas to fuel mixture) cures the stumble off of idle.
    Wouldn't that indicate that you need to be richer off idle (not leaner).
    Hopefully a carb master will chime in!
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  5. #4
    Senior Member SportsterDoc's Avatar
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    Quote Originally Posted by Donzo View Post
    ...You may want to try 1 1/2 turns out as well if you are riding at 9000ft regularly...
    What is your mixture screw setting, now?
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  6. #5
    Senior Member Fred's Avatar
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    I believe 2 turns was stated in post #1 for the current setting of mixture screw.
    A year ago I would have said a 122 main seems a bit too lean.
    Then elime, who really know his TWs, has reported success with even smaller jets. No single solution fits everyone’s bike.
    However post #1 was a bit confusing as to seeming conflicting reported effects of the choke. For clarification does the “runs crappy trill I push the choke in” mean the bike runs acceptably once warmed up and the choke is turned off?
    littletommy likes this.
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  7. #6
    Senior Member SportsterDoc's Avatar
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    Quote Originally Posted by Fred View Post
    I believe 2 turns was stated in post #1 for the current setting of mixture screw.
    Thanks, Fred.
    Guess I did not fully absorb that post!
    littletommy likes this.
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  8. #7
    Senior Member old w/??'s Avatar
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    I read it as stumbling off idle (pulling away from a stop) - then runs fine. But if he starts with the choke out (on) it does not stumble off idle (pulling away from a stop); but then runs crappy at speed - unless he then pushes the choke in (off).

    He needs a bar mounted, thumb activated choke so he can turn it on every time he comes to a stop; and flip it off once he gets going. Sorry DtN; folks here will get it figured out .
    littletommy likes this.

  9. #8
    Junior Member PowerMax's Avatar
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    If you need to start off from idle with your choke on, you need to go up one size on your pilot jet. You obviously need more fuel down low. I think the rule of thumb is if you need to turn out the idle mixture (air/fuel) screw more than 2 turns, go up one size on the pilot jet.
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  10. #9
    Senior Member Tweaker's Avatar
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    The choke is an enricher valve. He has tuned the bike to be leaner so what is happening is normal if not at altitude. Is it running like this at 9000 ft? What year bike too?
    littletommy likes this.
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  11. #10
    Junior Member DicktheNick's Avatar
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    Sorry for the delay, been off-planet the last few days. I live at 9000'. I ride at 9000', down to maybe 8000, as high as 9500. Bike is not leaving the mountains so trying to optimize it for up here. I'm also confused that it idles better with the choke on until it's off idle and revving, but not sure where to go from here. It ran the same before I changed the main jet down to 122 from 126. Also when I removed the plug to adjust the pilot air screw, I found the thing seated all the way in; I could only turn it out.

    I've got some time off now to look into this further. I think I'll put a TTO tach and temp gauge on it, would like to know what rpm it's running and how long it takes to warm up. Thanks for all the responses and I apologize for not getting back sooner.
    littletommy likes this.
    Dick in the Aspens
    2017 TW200 1995 KLR650
    1978 DT175E 1974 GT80A
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