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  1. #1
    CB750 New Member drmccart's Avatar
    Join Date
    Apr 2019

    Diagnosing CB 750k issues (1979)

    Hi All,

    I bought a '79 cb750 last year and was able to get it running. However, I am having a lot of issues and I dont really know where to begin. My biggest issue that I am trying to solve for the moment appears to be a problem with the carburetors. Currently the bike does not start unless the choke is all the way out, and even then, requires a bit of throttle to keep it from dying on me. However, once the engine is hot It runs no problem ~hour. After an hour of riding, the engine idle is really high (no tachometer but if i had to guess it would be approximately 2500 rpm ish range?). I'm also going through spark plugs like its my job, so the engine appears to be running very rich.

    Im sure there is a lot wrong, but I would appreciate any suggestions on where to start.


  2. #2
    CB750 Enthusiast NicksHonda's Avatar
    Join Date
    Apr 2018
    Sacramento, CA
    Start with the basics.

    What is your compression on each cylinder?
    What do your plugs look like? When were they last changed?

    While the carbs seem to be problematic and easily get junk in them, I would confirm the basics are good first.

    Are you sure you're running on all four cylinders?
    Sometimes the coils miss, or could be a bad wire/spark plug.

    Good luck.
    Havin' Fun in Sacramento!

    2006 BMW R1200RT
    1979 Honda CB750L

  3. #3
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Fort Worth TX.
    Like said, low compression makes everybody go after the carbs because they are CV type and they quit lifting the slides when the engine draw dies from lack of compression, which ties directly into valves set correctly and nobody ever does that either.

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