I remember SU carbies had a part that was pulled down to work like a choke. It moved the tapered fuel needle downward richening up the mixture. I think they also had a slot /breather where the bowl was bolted on that would spew out fuel if the float got stuck down.Didn’t early Holdens or cars of that vintage have carburetors that had a bleeder valve as well. From memory maybe it was on the underside to let fuel out of the carby when flooded? I’m not a rev head and testing my memory here.