Topic: Carb misting gas out of intake side, and cylinder not running

[nateweisiger02]

I used to have a 78’ CB750 and used the website for help when I didn’t know what to do. I have sold that bike after it was all fixed and got another bike, 1971 CB350. I didn’t know where else to ask for help so I figure I’d throw something in here to see if anyone has had a similar problem.

It hadn’t run in about 20 years, but have done some work to it trying to get it to run. Right now, it is only running on one cylinder. It will run non stop with cylinder 2 spark plug out, but only about 5 seconds with it in. It sounds the same both ways though. On cylinder 2, there is spark, and it is getting air. I sprayed carb cleaner in the intake and that didn’t do anything so I don’t think gas is the issue. It also mists gas out of the intake side of the carb. I will say, I stripped the spark plug hole but rethreaded it, and also messed with the valves. I know intake valve is a little looser than what it should be so I’m tightening that today. Any advice? What could be my problem?

[HondaMan]

The CB350 has unique carbs. They have some rubber diaphragms that contain the vacuum (from the engine side of the carb) to lift the slides (RAPIDLY) when the throttle is changed. If these diaphragms get holes in them, they don't move rapidly (or at all). This makes the engine spit back out the carbs, usually on the side opposite where the worst diaphragm is located. When BOTH are cracked, the bike is really hard to start and won't respond to the throttle, about like a cat on a leash.

Also: the OEM air filters must be used with these carbs, which is why you can still buy them today. There is a little tunnel behind the air filter(s) that connect both of them together: it is vital that the filters have a good rubber seal around that tunnel so both side of the air filters are connected. If someone fitted velocity stacks or 'pod' air filters to that bike, it didn't get ridden very far before it would not run anymore.