MY 1996 250 TRAILBOSS(2- STROKE)MAKES A NOISE AFTER IT HAS WARMED UP.AT A CONSTANT THROTTLE SETTING OF ABOUT 1/4;IT SOUNDS LIKE DETONATION OR A SLIGHT PING.IT GOES AWAY IF I INCREASE SPEED FOR A WHILE.BUT THEN COMES BACK.THE ENGINE IS STOCK WITH THE EXCEPTION OF A UNI FOAM AIR FILTER.I HAVE A 40 PILOT JET,AIR SCREW IS OUT NOW TO 2 1/4 TURNS,NEEDLE IS 2ND FROM TOP.PLUG SEEMS TO BE FINE(BR8ES).I EVEN INSTALLED AN AUXILLARY FAN KIT.I KNOW THAT THIS SOUNDS LIKE I AM TOO LEAN,BUT EVEN AT THE STOCK SETTINGS IT DOES IT.I THOUGHT OF CHANGINGING MY 40 PILOT FOR A 35,SO THAT I COULD TURN THE AIR SCREW BACK IN TO 1 1/4.I AM STUMPED!!!!!