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Hi guys!

I could use the some herd wisdom in solving what I think is a carburetor problem. I bought myself my first bike for Xmas 2017, a cafe-style '74 CB360. It was a daily commuter for the guy I bought it from so naturally it kicked over and ran fine when I bought it. But because I couldn't leave well enough alone I decided to do a carburetor cleaning and rebalancing as a learning experience figuring I had the whole winter to get the bugs ironed out if I broke something. So of course I broke something. In an effort to get the carb float exactly in spec I bent it beyond saving and after an embarrassing number of attempts to bend it back into spec and not flood the gas chamber I gave up and ordered a replacement. Now my gas chamber no longer floods and the bike successfully starts. However, when I start it up it displays some weird idling behavior I'm hoping y'all can help me diagnose.

When I kickstart the bike with the choke on and an artificially rich air/fuel ratio the bike idles fine - no stalling, no sputtering, no abnormal revving behavior. However, the moment I ease off the choke to add more air to the mixture the engine revs quite high (>4000 rpm) and stays there. This behavior is consistent whether I try to take the choke off right at start up or give the bike 5-10 min to warm up, whether I throw open the choke suddenly or try to ease it open by degrees so the bike has a chance to adjust. No matter how I try to cajole it into proper idling, the moment it gets any air it revs like mad.

Seeing as the bike was running fine before I cleaned the carbs and no tubes and hoses were taken apart, nor were any carb screws adjusted during my cleaning, my best guess is that extra air is getting in through the carb manifold somehow to produce a lean air/fuel mixture causing the high revving behavior. When I checked I did see some cracks in the right carb manifold, but those would have been present prior to my carb work when the bike was working fine. So unless my detaching and reattaching of the carb body caused those cracks to become perforations which now let in excess air I can't think of anything else that would've changed from before my carb cleaning, when the bike ran fine, to after. What do y'all think?

Appreciatively,

cyrano
 

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I am trying to understand how you could have done a proper carb cleaning and include this statement in your review of the work:
nor were any carb screws adjusted during my cleaning.

If you did not remove the adjustment screws while cleaning how did you make sure there was no debris in the passages?
My guess is you have may some internal clogging that is causing this issue.

Also your other statement:
I did see some cracks in the right carb manifold

YES - Removing and replacing the Carbs WILL cause those cracks to get worse and create air leaks which can cause your symptoms.

If the carbs is the ONLY thing you touched and after you have these issues, the problem is related to the work you preformed.
 
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