I have a Troy-Bilt weed-eater that has giving me problems for a while. In the third choke position it would rev up and slowly but surely, stall out. So today, I decided I would tune it up a bit and try to get it running right. I cleaned the air filter and for good measure, took apart the carb and made sure all the components were in good shape. And after this, there really wasn't much of a change in how it ran, so I went ahead and replaced the spark plug as well with a First Fire. The owner's manual said to gap the plug at .025, so I did. Now the engine seems to be running better than before, a little less boggy. But it keeps jerking, like the plug is misfiring, and then after moving the choke to position 3 it dies after holding on the throttle for a while. Can someone help me?!