gonna sound stupid to you but check the exhuast system also and make sure no blockage.. friends blaster ( my wifes not) did the same thing and there was a mouse nest blocking the pipe
yeah i took apart the carb today cleaned it with carb cleaner...used an aircompressor and it has a new spark plug...is it possible it needs new jets??
could also need a rebuild.. if the rings are toaste your loosing compression which will make it hard to start, and not want to stay runing or rev.. my buddys yz125 did that.. head and base gasket leaked.. so loosing compression
i could see through the jets..they looked ok...it has been sitting for a while so the gas isnt fresh...and if this helps it is leaking some oil and exhaust smoke does come out around the head