I have an A50 1968 that is a real bear to keep running. This applies to warm days and cold days. Someone, a BSA expert, claims they are very coldblooded and needs a lot of choke. It starts in a few kicks if I completely cover the single carb with my hand but even so will not stay running. If i remove one finger it dies instantly. I put on a premier with a #19 pilot and a #3 slide, no change. I can rule out an air leak at the flange, have not checked the single carb manifold joint to the head. Is there any truth to the idea that they need lots of choke for quite a while warming up? I usually remove the choke assy. Nortons and Triumphs do not need it.