Hi there, here s some information XT500 81 new 540 kit and head job done recently (was working very well on another bike) new points and condenser new timing chain stock XT exhaust Uni Foam air Filter stock carb start well cold on 2nd kick with choke on does not start at all hot with choke off but does start again with choke on...but i m getting a lot of kick back in fact...even after "purging" the cylinder few times. the main symptoms is: the engine died if stays at idle...it looks like it s chocking from too much or not enough air/gasoline? a lot of back fire seems to build up even at idle and getting worst when reeving up. reeving up very nicely though when the engine died the spark plug looks good with no carbon deposit or even trace of fuel on it. i tried to adjust the air screw mixture and the idle screw.. i tried to change the advance... i tried with another carb... valves are on the loose side... i cleaned the carb and all air/fuel passages Thank you in advance.