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Thread: Idle hangs up

  1. #1
    CB750 New Member Dakottaschumm's Avatar
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    Idle hangs up

    I have a 1980 cb750c. I got it from a guy for 575 dollars and he told me the carbs needed cleaned. Cleaned the carbs and found a vacuum leak. Got new boots and now there is no vacuum leak. The problem now is that it doesn't idle very well and if you rev it it will hang up at about 5 rpms and won't come down. I tried turning the idle down and the bike just dies. So I'm not sure if it's just a carb sync problem or if there is still a vacuum leak somewhere. If anyone can give me some advice I would really appreciate it! Thanks!!!

  2. #2
    CB750 Addict tommycarl's Avatar
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    How about a little more info please...

    Stock carbs?
    Stock air box or pods?
    Stock paper air filter?
    If stock air box and filter, is everything on (air box, crankcase vent hoses) and all covers tight?

  3. #3
    CB750 New Member Dakottaschumm's Avatar
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    It has stock carbs but aftermarket air filters.

  4. #4
    CB750 New Member Dakottaschumm's Avatar
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    The carbs are stock but the air filters are after market.

  5. #5
    CB750 Addict tommycarl's Avatar
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    It sounds like you have pods... 4 separate smaller filters, right? If that's the case, you may not get a whole lot of help because from what I've heard, the DOHC stock carbs are very very hard to get tuned, if they can be tuned well at all. You'll likely hear from most that you shouldn't use pods on these carbs... although you might hear from a few that they work just fine.

    As for me, I only have experience with one DOHC with the CV carbs, and they were a nightmare for me even with the stock air box. It was my fault, I'm sure... I cleaned them and thought I did a good job, but it took me 6 times to actually get to an apparent dirty spot(s) that I kept missing. Heck, I had the carbs on and off so many times I got good at it! In the end, the bike ran very well, but it sure was frustrating.

    Sorry, but I'm bailing out on you... maybe someone else will chime in.

  6. #6
    CB750 Member ciaochaz's Avatar
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    Howdy,

    Did you sort this out? Mine is doing the same thing. Thanks for any help.

    Charlie

  7. #7
    CB750 Guru amc49's Avatar
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    Vacuum leak or the carbs way out of sync. If you DO have pods that is not the issue but they will make other trouble for sure.

  8. #8
    CB750 Member ciaochaz's Avatar
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    K.I.S.S. All I had to do was tighten the bands on the intake boots. Too much air. Viola!

  9. #9
    CB750 Guru amc49's Avatar
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    The DOHC is well known for cooking those manifold joints to crack and no amount of tightening will touch that, many have tried. If the engine has ever had carbs yanked to stretch them I can practically guarantee it.

    If they are new parts fine but old likely will not seal.

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