Keihin Carb Body Little Brass Vent Disk question.

KMan

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Rebuilding a set of Keihin 7A carbs and noticed #1 carb - i.e. carb with choke lever - is missing one of those little brass vent disks. Not sure if I did it when blowing out passages with my air compressor or if it was missing all along. It's not the disk in the passage that goes to the air vent line. It's the one on the other side of the jets. Anybody know how critical this for carb / bike operation if I don't replace it? Anybody know a source for these disks? Can I buy them separate anyhere or do I need to scavange one from another carb body?
 

amc49

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Maybe you should pic it. I for one work on all types of carbs and have not a single clue as to what you are talking about.
 

KMan

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Pics attached. They're a little cloudy...didn't realize how much the lens fogged up from outside humidity. The disk is held in place by several tabs cast into the carb body in the opening for the air vent passage. I opened up #4 carb and that's the same - single disk, #2 & #3 have disks in both openings.

Answering my own question...they're there to meter air return out of the float chambers. #2 & #3 have two because the second passage is used to link float chamber venting with #1 & #4 carbs. In #1 & #4 the second passages dead end so apparently Keihin didn't want to waste the brass.

DSC01936.jpgDSC01937.jpg

Don't know why Keihin went cheap...other non-CB750 Keihin carbs I've rebuilt have had both disks installed even though the passages weren't used all the time. Curious whether other CB750 flavor Keihins beside the 7As are set up similarly.
 

amc49

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They will simply be vent restrictions serving as baffles. To slow down venting and possible overflow that is an emission issue from fuel sloshing around in the carb bowl when you lean the bike over hard. Size the hole in center carefully using small drill bits and put anything up in there you want with a same sized hole in it, or pull them all to equalize the venting to keep jetting on and suffer the possible fuel leakage, may not do it at all based on your driving style. Them being uneven is not noticed at normal cruise light load but you might get erratic carb action between the carbs at like wide open throttle, when they really need to all have the same size hole there.
 
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