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Thread: 74 cb750-4

  1. #1
    CB750 Member mrbobaz1's Avatar
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    74 cb750-4

    Hello, I have a 1974 750-4 with the wiring all screwed up. My problem today is I got the motor to fired up but no spark at #1 or #4 cyl. I changed to a different coil pack and the same problem 1 and 4 no spark. HELP

  2. #2
    Moderator dirtdigger's Avatar
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    Has to be and issue with the points or wiring for that coil.

  3. #3
    CB750 Member mrbobaz1's Avatar
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    good morning, both points are getting spark. all the wiring is in good shape.

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    Moderator dirtdigger's Avatar
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    Points dont get spark if they are you have issues. First post says wiring all screwed up now you say its good?? Points, wiring,and coil/plug wires/plugs are only things that will cause issue with no spark....has to be problem there, nothing else in the system. Have you verified point gap, dwell, timing and that the point contacts are clean?

  5. #5
    CB750 Member mrbobaz1's Avatar
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    what I meant is that the wiring was all loose[screwed up] no tape around any of it, but all the wire themselves are in good shape. The points are getting electricity to the both of them. no spark out of #1 spark plug wire or #4 spark plug wire. With the motor running on #2 and #3 cyl. I put a test light on the blue wire to the one point it lights up but when I put the test light on the yellow wire the motor dies.The black and white wire is hot.

  6. #6
    CB750 Addict Dave's Avatar
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    Your doing the right thing by asking questions but, from the questions you are asking, you don't currently have the knowledge needed to successfully troubleshoot a dual point ignition system.

    Assuming you have the intelligence, patience, and motivation to learn what you need to know in the end your going to figure out the stock ignition is very troublesome and time consuming to keep functioning properly.

    You'll save a lot of time and effort and end up with a much more reliable and better preforming bike if you just spend the $210 now for a Pamco ignition kit. (the one that includes coils and caps)

    https://www.cb750supply.com/products...ions-and-parts
    96% of the time I edit my replies so check back for updates if it isn't at least an hour old

  7. #7
    CB750 Member mrbobaz1's Avatar
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    so what you're saying is you don't know the answer either.

  8. #8
    Moderator dirtdigger's Avatar
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    I do know, it has to be points/condensor, coil/wires, plugs or the bike wiring, the only things that will cause no spark on mating cylinder pairs. Did you check the things I said to check? I suggest starting over with the basics. Points are very simple, they are just a switch, if its not making your light turn on and off as it turns over you have a point issue. The member that posted above was just trying to convey (maybe could have been a bit more tactful but then again words get taken out of context online and we should learn to take them for what they are and not get offended) that if you cant trouble shoot points or dont have the correct tools to do so you probably wont be able to fix it on your own and should find someone with experience with points. More then likely your points are worn out and should be replaced anyway as they are a wear and maintenance item to be checked/cleaned/adjusted every 3000 miles. The whole system is the point plate, the coil/wires, plugs, power to coils...you swapped coils so probably not the issue, one bad plug can cause both to not fire but probably not the issue....so you got the points and the bike wiring left.....do with the information what you will not sure what else I can do to help you.

  9. #9
    CB750 Addict Dave's Avatar
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    Quote Originally Posted by mrbobaz1 View Post
    so what you're saying is you don't know the answer either.
    I'm saying you have not provided enough of the right information to give you an accurate answer. Dirtdigger has provided all the troubleshooting information necessary.

    I'd crank the engine with the plugs out 1st (plugs out so it spins faster) and see if there's spark across the points, that's a sure sign the condenser/s are bad (assuming the points are not bad and are properly adjusted and the advance mechanism isn't worn out and wobbling all over, etc etc). You'll find OEM condensors are quite expensive and aftermarket ones are crap. I believe AMC says you can use the old style chevy condensors and they are better quality but I never tried it personally. (If AMC says it's so, I believe it, I just can't remember where I read it)

    My point is by the time you've learned everything you need to about that ignition system, your going to realize it's crap and probably want to replace it with an electronic ignition anyways. Just trying to save you some time.

    That's my grandson sitting on my custom 1974 CB750K in my profile pic. I already went through everything your just starting on with it. I got that dual point ignition working as good as possible only to realize it was crap. I finally put a pamco in and have never needed to touch the ignition again.
    96% of the time I edit my replies so check back for updates if it isn't at least an hour old

  10. #10
    CB750 Member mrbobaz1's Avatar
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    my 74 CB750 has been sitting for twenty some years. Just to let you know, with a little more checking one of the points was out of adjustment. After adjusting it and rebuilding the carburetors the bike fired right up. I wanna thank you guys for your help.

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