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  1. #1
    CB750 Member John Luke's Avatar
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    Help with carbs on 81 CB750C

    I am working on a 1981 CB750C. I have a 4-1 delkevic exhaust on and the original air box. Can anyone tell me what jets and air/fuel mixture settings yall use? It seems to run okay. But when I give it throttle the rpms lag a bit b4 going down and there is a little bit of backfiring. Any help would be great. I have stock jets in rn.

    Thanks!

  2. #2
    CB750 Enthusiast NicksHonda's Avatar
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    Usually you would need to go up about 10 or so in size. It's mostly trial and error tho. Good luck.
    Havin' Fun in Sacramento!

    2006 BMW R1200RT
    1979 Honda CB750L

  3. #3
    CB750 Guru amc49's Avatar
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    That will likely be too much for a fully muffled header with OEM airbox, CV carbs LOATHE extra jetting unless it has a definite purpose, they make the most power slightly lean. They greatly self adjust to provide the automatic re-jetting on the fly too. The ten number can be good for direct lift carbs, these are not those at all.

  4. #4
    CB750 Enthusiast NicksHonda's Avatar
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    Oops my bad. Sorry

  5. #5
    CB750 Guru amc49's Avatar
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    I've found a good number is 75-115 on the 2 jets BUT the motor MUST be sound and pulling good vacuum at the slides or that will be likely too much jet. You simply cannot overemphasize how much compression figures into these to let the slides drop to make any added jetting cause you trouble and then people dump the OEM airbox to make things even worse. With that number the exhaust must be a header and it cannot be a crap design one either. 4 pipes and a collector do not a header make. It's too much jet for an OEM 4 into 2 pipe setup.

    Most people never question the compression and why so many have utter fits, then they go up in jetting due to the common misconceptions and it gets worse. The valves on these were rotten even when they were brand new, the heat treat on them is beyond description in how crappy they are.

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