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Adjustment question on carb

Discussion in 'Fuel / Air' started by Mike manson, Apr 23, 2018.

  1. Mike manson

    Mike manson Well-Known Member

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    I rebuilt carb put all new gaskets and stuff in the bike fires up great no backfiring at all the accell pump set good has good throttle but when I shut bike off it has like a cough do I need more fuel


    Sent from my iPhone using Tapatalk
     
  2. Sven

    Sven Well-Known Member

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    I'd run the low speed screw out 1/4 turn at a time. Yes, sounds lean so it needs more fuel. And that means with a hot engine, meaning, 1/4 turn out, get the bike hot [which expands the air so it leans out] and then turn it off. Still pops with a hot engine, then 1/4 turn out again. Say it gets worse. Then remember your initial turns, start from where you first started and then run it in 1/4 turn to eliminate the pop.

    It goes something like this with the generic carb:
    1. If the air screw is on the air cleaner side = Air.
    2. If the air screw is on the head side [past the slide] it controls = Fuel.
     
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  3. Little-Boo

    Little-Boo Well-Known Member
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    Since your Carburetor has a butterfly and not a slide I guess the adjustments mentioned above are out the window. What size intermediate jet are you running. It sound like you bike is running lean. If you are still running the stock 29.5 change it out to a .031, especially if you have changed the exhaust. If you changed the exhaust you should have re-jetted your carb then. If that is the case I would do the .031 intermediate and change out the main to 74 or 76 if it hasn't been done yet.

    Carlos
     
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  4. SEAL-rider

    SEAL-rider Active Member
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    IMG_2801.JPG Pull your plugs and post a picture. A stock 2005 is unlikely to need more than a .295. Mine runs rich with .31 and I have cam and pipes. These are mine with a .31. Definitely rich at idle, midrange is great. BTW this is California gas which sucks.
     
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  5. BWG56

    BWG56 Guru

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    They look good to me, if anything slightly lean:2cents:
     
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  6. SEAL-rider

    SEAL-rider Active Member
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    The heavy black to the top of the threads is an indicator of rich idle. Then things lean out. I went back to .295 and the threads are now light brown and the rest is light brown/grey. I have a .65 Thunderjet on the top end and if I go bigger, my MPG goes South fast. I just need to keep it below 4500 rpm. Above 4500 and more fuel is needed demanding a .80+ Thunderjet.

    It was not clear from Mike the OP if he has an E or G carb. My intermediate jet was a .295 on my original E carb too.
     
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  7. SEAL-rider

    SEAL-rider Active Member
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    That is a simple explanation. More can be extrapolated.
    Plug-2.jpg
     
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  8. Sven

    Sven Well-Known Member

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    Makes me think of my shadetree 4-in-1 I mickey moused parts. Used a short galvanized pipe with threaded ends. Capped the one side of the pipe and closed off the hole at the collector split. Once I removed the mod, I unscrewed the cap. The pipe was carboned to shit all the way down its walls. The cap had no trace of carbon at all. So I said to myself, 'shitdamn, looks like a spark plug read to me?'

    The inside carbon contact with the plug's wall is the same as that plumbing pipe. The porcelain remains hot enough to burn off any carbon per say. The tip means jackshit when reading a plug. You need to look all the way down at the end of the cap per say. Say that's a tube with a cap at the end, which means the end of the porcelain. There is where you get your color reading:
    1. Brown = Rich.
    2. Tan = Best all around performance.
    3. White = Lean Is Mean.
    4. Gray = Race ready.
    And data is where/how you read a plug... way down in there with a spark plug viewer.

    Porcelain Nose Read:
    a. Look for gray specs burned into the porcelain = Detonation at the plug to piston's most closest point, or kinetic meets this side of TDC. aka. 'knock.'
    b. Look for spark jump from center electrode to side electrode = If not, it's sparking inside/outside the porcelain, aka, 'engine miss.'
    c. Look for wet gas or shiny oil on the porcelain = Can show a spark failure to worn rings or guides filling the combustion chamber.

    Outside Threads:
    I. Dry = Color means nothing. It's all about a healthy engine.
    II. Wet = Oil is being compressed up the threads and that comes from rings/guides.
     
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  9. SEAL-rider

    SEAL-rider Active Member
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  10. Sven

    Sven Well-Known Member

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    https://www.hdforums.com/forum/atta...stock-carb-89-fxstc-keihin-butterfly-carb.jpg

    If I'm not mistaken and looking from here, 12 is on the head side, yes? IF we look at the (quote) butterfly, would you agree the slant of the butterfly is angled directly above the hole for the low screw? If you wanted to bring the idle down, wouldn't you more upright the butterfly to close the hole so the idle comes down? Would you agree that fuel comes out of that hole, not air? Isn't the slanted angle the air?

    Does 1 and 2 still apply? I like to see how clean uses windows are, use looking hathatrick blowout. Make sense?

    Signed,
    NOLTT
     
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  11. Sven

    Sven Well-Known Member

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    Mine was more a basic peek at the internals via a plug read, not a race profile. Note the line going in... 'trailer the vehicle back to read a plug.' If the timing didn't change, nor the jetting, it's this side of melting down the plug via the porcelain used. The less porcelain, the less retained heat. That's the cooling factor, not the side electrode color per say. You are handcuffed to so many heat ranges trying to chase a side electrode heating up ideally. Besides, those are not race plugs. The porcelain looks too long and hot for racing. The center electrode is not fine wire anshit. The gas used can change color from pump to racing blends. And too, you'd have to throw heat at the engine so you'd have to run a few laps, and then kill the engine at redline/top gear/most load and all that sustained speed. Now read that new plug down at the porcelain.

    The flat part where the side electrode is welded to: that color can be found down at the porcelain, at the exhaust valve, the exhaust port, and the tip of the muffler. That's 3 open circuits [at WOT} contributing to the vacuum suck = AFR. This is more race bike color(s) with little hours and kept at high rpm for that amount of time. No way to tune a street bike with that kind of rpm thrown at it. The BD works within a certain range and if one calls out a number for the jetting, this is more hit and miss 'forum tuning' with a suggested setup. It's seat of the pants from there on out.

    In other words, doesn't knock under load; doesn't overheat, doesn't fall on its face (lean), rather chirps the tire when you wick it open and keeps pulling from there.
     
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  12. pknowles

    pknowles Getting better by the day...---... GURU
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    "Forum tuning":). Welcome back and thanks for sharing:oldthumbsup:
     
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  13. pknowles

    pknowles Getting better by the day...---... GURU
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    This goes right along with "Bench Racing"
     
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