I picked up a Poulan 255 Pro for $10 that I can start and run wide open for about 20-30 seconds and then it just dies. Then I try to restart and it won't start until it cools down. I took the carb apart and cleaned it out, diaphragm and rubber parts not stiff or brittle. I don't expect much from this saw, but it should stay running. What do you think is wrong?