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  1. #1
    CB750 New Member Philmor's Avatar
    Join Date
    May 2020
    Location
    Edmundston, Canada
    Posts
    1

    Firing on 3 cylinder

    So my dad bought this 81 cb750 a couple years ago and he always had trouble with it, so he gave it to me and we find out that it was only running on 3 cylinders, cylinder one wont fire, so I replace all the spark plugs, still not firing, so i removed the spark plug on cylinder that is not firing and the spark plug look like new compare to all the other! I have a spark but it dont seems to hsve fuel going.. I've check the compression and i got around 120 psi on each cylinder, i need some help for this one, thanks!

  2. #2
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,909
    120 is getting pretty low, normal being 170 and 100 is a dead cylinder that even firing will not make power. Commonly it comes from nobody ever setting the valves then they burn to leak.

    If the plug is coming out dry you likely have no fuel to it, the carbs lean toward doing that pretty bad too. The idle jets stop up and sometimes can be cleaned 3 times and still not opened up.

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