My 77 xt 500 had low compression and has been rebuilt. The valves were ground and adjusted and the carb was rejetted. The carb had a 310 main and 25 pilot and now has a 185 main and a 30 pilot. I live in Salt Lake City (4200FT). The points and condensor were replaced. It starts well when cold without choke and it kills after idleing for 5 minutes and then will not restart unless I wait for 30 minutes plus. What am I missing??? Please comment.