I have a 1974 Vespa Ciao. When I try to start it with the choke on and not pulling on the throttle, it doesn't start. I have to pedal and have the throttle cranked all the way to get it to start, and then I have to rev it for a while so it won't stall. Is this normal for a 2-stroke engine? Also, sometimes when I'm at a red light for a little while, it will stall, and I will pedal through the intersection to start it. It usually takes about 100 feet to start up, and it usually backfires right when it starts. I know when it is going to start because it backfires right beforehand. Any suggestions?