Leaky Carbs on a 1981 Honda CB650 Custom

Great article on carb cleaning….very explicit. I am a first time owner (not so new rider) of 81 honda cb650 custom. It was reasonably well maintained. has 55000 km. It appears I may have carb issues, but would like your opinion before I follow your advice on cleaning. Fuel is leaking out the bottoms of the carbs (in line 4). However this only started to happen following full choke for extended period of time while cold idling. while tightening exhaust from replacing copper o rings at manifold. Also had noticed I left the petcock in the open position for a couple of days after riding. Which by the way i noticed does not fully prevent fuel from entering carbs ( petcock not shutting fuel off completely) as it still drips regardless of setting to off position. Could the carbs have over fillled due to petcock and choke issues….or are the floats likely in need of cleaning. And yes there had been a fair bit of rust in the tank, although I was pretty diligent at removing prior to this fuel leaking issue as I removed for mantenance. There is also an in-line fuel filter reccommended and installed by previous owner due to rust in tank. It seems to capture any residues. Can you offer sugestionsor advice on how to proceed. The bike was running very well and in spite of fuel dripping from base of carbs was still running and idling good. I appreciate your time and efforts in anything you can offer….happy trails….take care.

Thanks for the post.

Leaky petcocks are very common on older bikes. Over time the gas will dry out the rubber diaphragms inside the petcock. It’s easy to replace the rubbers inside the petcock. Rebuild kits can be bought all over the place for under $15.

As for your #4 carb leaking through the overflow – also common. You could have a couple minor problems causing that. Your float level might need to be adjusted, the float pin might be dirty and sticking, and your float needle might be worn and leaking. All three are easy to take care of, you’ll just need to remove the carbs and inspect them.


Evan Fell

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