if it's a manual choke, it'll be the choke links sticking, more than the carb itself ... the Roch B manual choke has a spring on the choke,
#21 shown here, and the YF may have similar,
maybe this one - but also see
original documentation here, one pic [page 2 of "Carter Carburetor Corporation Form 3526, December 1949: Service Procedure, YF Downdraft Carbureter"] shows a coil type spring [#21] as part of the choke .... the YF is a good carb, you should be able to get it working right, and do replace the nail with the correct part
edit: found a pic showing a
spring on the choke linkageBill
