Just had a top end done. Son took the bike to ride yesterday. He said bike fired up really easy. Rode it around slow for a lap and said it felt really good. When he went to get on the gas bike died. He couldn't get the bike to start back up. When I got home kicked and kicked and finally got it going. When I wacked the throttle the bike died. Took it back to the shop today. Got it started with a lot of kicks and the mechanic rode it and when he got on the gas it died. Any ideas what could be the problem?