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  1. #1
    CB750 Member Jayboy74's Avatar
    Join Date
    May 2013

    1991 cb750 wont start , several electrical issues

    Hello Everyone.

    Let me start by saying , Thanks for the great forum , I have read a few post and have been able to do a few repairs on my bike thanks to you guys, I am new here and after researching the issues with no luck i am going to post what is going on in hopes of getting this bike back on the road.

    What I have is a 1991 CB750 that has sit or 4 years. It was wrecked and had a bent front wheel ( just replaced it ) busted headlight lens and no bulb mounting tub. I am to the point were i am trying to start the engine but i am getting no fire. This bike has been monkeyed with and its hard to tell what the previous owner as done to it. Here are the issues i am having

    The start button does not work, Instead the previous owner put 2 wires on the coil that you touch together to start it.

    The head light is missing ( is it part of the circuit and will it prevent he bike from starting?)

    How can i test the kill switch? Can i bypass it to temporarily test for fire?

    The turn signals work strangly , If i push the switch in it will start one side blinking but its random as to which side. If i slide it to the left or right it does nothing.

    The gearbox is in neutral but the neautral light is not On , Will his prevent the engine from starting?

    Thanks everyone , I am looking forward to getting this bike back on the road.

    take care

  2. #2
    CB750 Enthusiast fourk's Avatar
    Join Date
    Dec 2012
    southern lower mich
    Dont know if this will help but T keep an extra wire hooked to my ignition plug to put some power to my 77 when the switch loses contact,that wire turns on my green light & fires my bike.

  3. #3
    CB750 Member Jayboy74's Avatar
    Join Date
    May 2013
    Thanks Fourk for the reply. Just to make sure when you say starter plug do you mean the wire that goes from the starter solenoid to the starter? If so thats the only way i can currently get my bike to turn over , I have a jumper wire that completes the solenoid circuit thus causing the starter to spin. My ignition switch seems to work , When i turn the key on the gauges light up.

    Does anyone know where to find a free online service manual for the 91 cb750 night hawk?

  4. #4
    CB750 Addict Dave's Avatar
    Join Date
    Sep 2012
    Headlamp don't matter.

    Street bikes don't have "kill switches". The only momentary buttons would be start and horn.

    "pushing in the switch" - Sounds like emergency flashers.

    Neutral Light - The bulb could be burnt out but the purpose of this neutral circuit is to keep the bike from starting. Usually the bike will turn over even if it is not in neutral if the clutch handle is pulled in all the way.

    You can find some nice schematics here but not the one you need most, the electrical diagram.

    With this many electrical issues you should really buy a manual. If the wiring harness is hacked up your best bet is replacing the entire harness.

    Edit: Just came across these, might find the one you need
    Last edited by Dave; 05-17-2013 at 01:15 PM.

  5. #5
    CB750 Enthusiast slowpoke69's Avatar
    Join Date
    Dec 2012
    Great diagrams, didn't dive into mine, did save it though, thanks.

    I recently found, my 1st order bit here correct and in good time. Brenda is a BIG help!

    I don't know if will have a new harness for yours, mine it's $90 bucks.

    Were I you I'd start with a new harness and roll from there, at least you know ALL thewwiring is good that way.

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