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  1. #1
    CB750 New Member GB75081's Avatar
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    CB750 KZ 1980 - Only firing on Cylinder 3!?!

    Good Morning All,

    First post on this forum, so Hi all!

    I've been working on my custom build of a CB750 KZ (which has an 1980 FA Engine) for a few months now. The bike was running on the standard airbox but no surprise, I decided to take that out and replace with pod filters. Post the tear down and rebuild the bike seemed to start and run fine (at a stand, if perhaps a little lean needing the choke to start). It sounded relatively healthy when running so I didn't check all cylinders until I came to actually ride the bike for the first time. I took it down the street and it seemed to bog straight down and require heavy revs to keep it alive. At the time I put that down to the pods, and that I may need to adjust the air/fuel mixture on the carbs (they have been cleaned during the build). After getting it back in the garage at home something has changed. It now won't really start and only Cylinder 3 is getting slightly warm, the rest are stone cold. I thought this odd as the coils are obviously in pairs, figured if it was a coil issue it would be 2 cylinders at a time working or not working(?). Anyway, I thought perhaps it could be the fuel not getting to the carbs effectively and tried spraying some starter fluid directly into the carbs to test how they would respond, got nothing.

    I've read a few threads now with similar sounding issues and many seem to point to poor connections on the wiring to the coils or something similar. I have not yet checked all these things thoroughly, but thought I would check in with the collective wisdom of this forum! The thing that confused me and made me think it wasn't the coils was the fact that one cylinder was getting warm!? Why would just one and not both cylinders on that coil be warm?

    Any advice much appreciated

    Cheers!

  2. #2
    CB750 Addict Wez_'s Avatar
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    I've been working on my custom build of a CB750 KZ (which has an 1980 FA Engine) for a few months now.

    What does the above statement really mean? What was it's original condition and "work" have you done? Background is much needed. There is a build thread from PDJones or something like that with a rat bike he wants to build. He had the same problem and ultimately he ended up just burning off what seemed to me like excess carbon and dirty gas. But without know what work was done and the current bike condition, it's hard to help you out. With the PODS off, twist the throttle and make sure you have a nice solid squirt of fuel coming from the accelerator pump nozzles squirting directly into the center of EACH carburetor. This isn't the only check you have to do, but it's sort of a "Final Test" once your carbs are all cleaned up and all the fuel circuits are cleaned and functioning correctly. It's a good start and easy to do when you have PODS on. If you had the stock air box, then I would suggest the same thing, but removing all the rubber/plastic is a pain.

  3. #3
    CB750 New Member GB75081's Avatar
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    Quote Originally Posted by Wez_ View Post
    I've been working on my custom build of a CB750 KZ (which has an 1980 FA Engine) for a few months now.

    What does the above statement really mean? What was it's original condition and "work" have you done? Background is much needed. There is a build thread from PDJones or something like that with a rat bike he wants to build. He had the same problem and ultimately he ended up just burning off what seemed to me like excess carbon and dirty gas. But without know what work was done and the current bike condition, it's hard to help you out. With the PODS off, twist the throttle and make sure you have a nice solid squirt of fuel coming from the accelerator pump nozzles squirting directly into the center of EACH carburetor. This isn't the only check you have to do, but it's sort of a "Final Test" once your carbs are all cleaned up and all the fuel circuits are cleaned and functioning correctly. It's a good start and easy to do when you have PODS on. If you had the stock air box, then I would suggest the same thing, but removing all the rubber/plastic is a pain.
    Thanks for the reply. All fixed. First thing I checked was the plugs and by changing for new plugs...all the work I'd done to clean and setup the carbs came to fruition.

  4. #4
    CB750 Addict Wez_'s Avatar
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    Great. We are here for you!

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