Mixture screw setting problems- and a flat spot in the carburettion ? - Page 6
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Thread: Mixture screw setting problems- and a flat spot in the carburettion ?

  1. #51
    Senior Member -alan-'s Avatar
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    Quote Originally Posted by 66Sprint View Post
    Just ONE QUESTION..... How is it that in all the work you (and your friend the mechanic) put in on those carbs no one noticed a missing main jet????????????

    (I got to know....Was it simply in the bottom of the bowl, having vibrated out?)...Yes, I know...TWO questions....
    Wasn't the mechanic, and can't even claim it vibrated out (though I'd like to) - this one was purely down to me. I brought all the bits home from the U/S cleaning, and sat down late one evening with a magnifying glass, a couple of screwdrivers and a set of vernier calipers for the float height. Only thing I can put it down to is while working through the build I got so focused with the minutae of examining every little hole and detail in all of the brass parts that I just got distracted and missed the fact that I'd left one of the main jets out

    I do remember looking through the box of bits and spares and debating whether to run with the 145 or 150 mains at one stage and going off to google for some info - and probably screwed up by forgetting I hadn't actually put both jets back in at that stage.

    Hey ho ..



    Every day's a learning day
    CB450 K5

  2. #52
    Sensei 66Sprint's Avatar
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    Don't know if this will make you feel better, but.....
    I once had to deal with a CV carb that would idle perfectly, or run wide open perfectly, but ran horribly anywhere in between....
    Turned out the entire slide assembly (spring/diaphragm/slide/needle) had been left out.........
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199

  3. #53
    Senior Member WintrSol's Avatar
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    I had the opposite discovery. I got a 305 Super Hawk cheap because it wouldn't pull, but idled perfectly. On this engine, the slides are pulled by the throttle cables. Seems someone had rebuilt the carbs, both at the same time, and swapped the slides; one worked, the other resisted and broke the cable. This is why we say to have one carb apart at a time.
    Rick

    Mine is a mostly 1970 CB450K3

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  5. #54
    Senior Member -alan-'s Avatar
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    Thanks guys - I almost don't feel so bad

    The daft part about it is I must have stripped and reassembled those carbs at least a dozen times by this stage. Thought I was at the stage where I could do it with my eyes closed. Apparently not..
    CB450 K5

  6. #55
    Senior Member -alan-'s Avatar
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    Well who'da guessed..these fine little engines do actually run better with all of the bits in the carburettor than with some of them left out. Carbs rebuilt, fitted, and all of the air-screws working as Honda intended. Test run shows the bike pulls cleanly from idle, accelerates hard up through the rev range, and keeps going all the way to the redline.

    I think it's time for a rest

    (Would actually like to do a bit of a summary/wrap up on my own experience with the low-running issue for anybody else struggling with it - but need to try to refine my own thoughts to see if I can pinpoint which of the changes / which particular combination of changes were more likely to have cured the problem. Might need to bounce some ideas off you guys to check whether the diagnosis and conclusions make sense first).
    Last edited by -alan-; 10-02-2019 at 12:25 PM.
    CB450 K5

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