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  1. #1
    CB750 New Member bretgs's Avatar
    Join Date
    Mar 2019

    1981 CB750c Gas Leak

    Hey there,

    Last year, I finally achieved my dream of buying a motorcycle. I picked up a 1981 CB750 in great running condition and just a little dull in some areas and had a blast.

    Near the end of the summer, I noticed some fuel leaking out of the second carburetor, and had some trouble starting. She would fire up if I gave her throttle with the choke open, but otherwise it was a bit of a struggle. Eventually, rough-starting turned to non-starting; I assume the battery was tired of my nonsense. I ended up draining the fuel from the bike, pulling the carbs out, and staring at them for much of the winter. I put them back in and pulled them back out a few times, enough that it doesn't seem like such a chore anymore. Though, if anyone knows the specs on the screw that is meant to hold the airbox back when you do it, I'd really appreciate the info.

    Anyway, today I pulled the carbs again and replaced the float needle on carb #2, as I had seen it was getting worn and my friends had mentioned that may be the issue. Put the carbs back in, added some oil and some new fuel, and lo and behold, she runs -- very roughly. Probably because I mucked about with the carbs, and I don't really know what I'm doing. The biggest problem though? Carb 2 is still leaking all over my bike.

    The leak doesn't even seem like it's coming out of the overflow. It definitely drips off that part, but it's the lowest part of the carbs, so that would happen anyway. If the bike is on the kickstand, it sort of pours off carbs 1 & 2 together, which makes me think the leak is much higher. Here's a video of my bike dumping fuel all over the damn place and then starting anyway:

    I'm hoping you guys can give me some recommendations on what to try next, or what the problem might be. I'm getting stuck. Thanks for reading.
    Last edited by bretgs; Yesterday at 09:13 AM.

  2. #2
    CB750 New Member bretgs's Avatar
    Join Date
    Mar 2019
    Ghost town over here, eh? No love for the DOHCs?

    I pulled everything apart again and found my problems. In reassembly, I had one carb bowl seated wrong, and my fuel line connection with my carburetors was not secure. No more leaks! So why was it running so rough? In short, because I mucked about with the carbs and jacked my pilot settings up. Finger tightened them, backed them out 1 1/4 turns, and lo and behold she runs beautifully. A little rattley, which I think is because it's a touch low on oil, but I don't want to change it until the filter comes in.

    Just thought I could possibly help someone else with my errors.

  3. #3
    CB750 Addict pidjones's Avatar
    Join Date
    Sep 2018
    East TN
    Adjust the cam chain tensioners and balance the carbs. That should smooth it out.
    "Love 'em all.... Let GOD sort 'em out!"

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