I have had a Poulan 2150 for 3 years now and it has been working well until now. I had to cut some fallen tree limbs, so I took the saw out of the garage. I replaced the fuel with a 40:1 mixture of fresh gas to 2 cycle engine oil. The chain saw is also filled with fresh Poulan Pro Bar & Chain Oil. The air filter & spark arrestor are both clean. When I try to crank it up, I pull the choke to full, turn the ON/OFF swith to on, prime the engine, and lock the trigger, all like the manual says. I pull the string and the engine cranks up and begins to idle. I squeeze the trigger and the chain turns. Then I push the choke in, and the engine immediately dies. Did this over 10 times. I tried to adjust the carb and screwed it up. So I turned the High and Low screws to 1 turn from stop point. It doesn't crank up at all now. What did I do wrong!! Help me please b/c my driveway has a tree accross it and I need to move it. Thanks