my friend has an 03 450 and it always pops on decel and is hard to start when cold and when warm. it also idles erratic, sometimes high sometimes low, sometimes snapping the throttle will bring a high idle down and sometimes not. so &%$#@!??? we decided to check the valves and found the intake side to be a little tight so we reshimmed and now they are right on. we also went through the carb and cleaned everything and found a 162 main and the needle on the 3rd from the top. we live in utah at 4000 ft. we then decided to repack the silencer just cause. we used stainless steel wool around after the stock steel then fiberglass. put everything back together and the carb setting back the same. now the thing really pops a lot after blipping the idle and the pipe got so hot after a few minutes it started melting the air box. it runs worse then before. I am thinking we might be a tooth off on the timing but am not sure is there anything else that could be the cause of this?? could it be the silencer with the new packing? what if the inner part of the silencer is broke and some of the inside isn't lined up. I herd something that sounded wierd when we put the silencer back together. I don't want to redrill the rivets out again unless I have to.