What is the brass pin behind the choke for

I don't know this carby in particular, but I agree that it looks like a vent. If that's the case, the vent is doing the right thing, but your float isn't. The float should rise up and seal the inlet when the bowl is full - if it doesn't seal correctly it will keep filling and start flowing out the vent.

Time to look at your float - it's either seized/broken so that it doesn't float, or the float seal needs replacing.

Ok so I adjusted the float on that side got her running took her out for a test ride and now she is running on one carb but she is not leaking out the vent anymore. Going to strip the carbs down and see what happens. She's about there though. Thanks everyone for all your advice.