My son has a Stihl MS310 chainsaw about seven years old. He hardly ever uses it so I would guess it only has 20 or so hours on it. It cuts well and starts pretty easy but after it warms up it will stall very easy and often. Then it is hard to start and when you do it will idle but when you hit the gas it will stall. My son has rebuilt the carb, new air filter, new fuel filter, new plug and tried to adjust the mixture. We also use Sta-bil and change the gas out often. Any ideas? Thanks!