stihl 041 gets hot won't throttle up,stalls?

stihl 041 runs good till it gets hot,seems to get hot too soon...after it's hot,it doesn't want to throttle up,may idle,but it cuts out when you try to throttle...sometimes it recovers when you play with the trigger,sometimes it stalls..i changed diaphrams and have been running hi-test,for about 5 years and a bit heavy on the oil mix..compression is about 150psi...i bought the saw new and has never been worked on and is not a production saw...please get back to me...thanks.

bill
October 2009