The International CBX Owners Association

So after a hibernation, I fired up my '82. It ran and idled fine, however there was gas spilling from both carb bank overflows. Plus when I rode it the mid rpms were missing badly. So I pulled the carbs. On the bench I pulled the 1-2-3 float bowls then turned the set over to find this o-ring sitting there on the bench under the carbs. I have accounted for the o-ring on the accelerator pump. There really aren't any other parts to fall out. Does anyone recognize this o-ring or where it came from? I might mention that the 4-5 vent tee is tattered and needs replacement. Does it have an o-ring in it?
The o-ring size is about 8mm od x 4.5mm id x 1.75 mm thick.

If all you did was remove the float bowls and I see that the accelerator pump o-ring is there as you mentioned, then, I can only assume it was lost/dropped/caught in between the bodies.
All the other o-rings are on the connector tube ends for the fuel delivery, accelerator pump circuit or the air vents which you haven't touched, yet.

We have all the parts in stock to do a complete rebuild including OEM spec vent Tees and OEM Keihin brand float needles (aka, no junk). Better quality and less expensive than any other supplier. Hit us up at sales@kmcarburetor.com for whatever you need/want.