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  1. #1
    CB750 Member powellskier's Avatar
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    1980 CB750K idle issues

    I own a 1980 CB750K w/ Vetter with 34,000 miles that I have been working on for far longer than I care to admit.
    (I also own an identical motorcycle with around 23.000 miles.)

    Without getting into too much detail, my problem is this: I cannot get this thing to idle. I have rebuilt/replaced the carbs twice, checked and rechecked valve clearance (.004 - .005) and run compression tests. Compression numbers are a bit low, but all my tests have been done when the bike is cold. The compression numbers are slightly higher on the 23k engine.

    While syncing the carbs with a mercury sync tool, I noticed that the 34k engine draws half as much mercury as the 23k engine. This tells me that my intake "suction" through the carburetors into the engine may be why I am having so much trouble running it at low RPMs. What do I need to do to remedy this problem? Do I need to tear it down and check the rings and seals + cylinder and piston tolerances? Any advice would be greatly appreciated.

  2. #2
    CB750 Addict Wez_'s Avatar
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    What about swapping the carburetors from the bike with 23k onto the bike with 34k and see how it behaves?

  3. #3
    CB750 Member powellskier's Avatar
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    I thought of that, but then I remember all the cuss words, aggravation, skinned knuckles, more cuss words and hassle of removing and installing these. (especially installing)

    I appreciate the response and I am leaning towards doing just that, but I think I will wait until this winter.

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