Hello! Yesterday I let my brother take my bike out for the day. it was about 34 degrees F in the morning when he fired it up. he said that he let it go with the choke for about 20 seconds then turned the choke off. he said that it idled just fine with out the choke so he took off in first gear. when he tried to shift to second he said that the bike died immediately and it has not run since. when i start it, it will only idle with the choke on and the idle is very poor and uneven, the bike is also backfiring when i try to start it. any ideas whats wrong? Thanks!