Hi, I bought a used Craftsman trimmer for cheap, unkown age, but pretty new as it has Incredipull feature. Sears Model# 316.791890, MTD model # 41ad770c799. I'd like to know what carb adjustments can be made on it? Basically it starts ok, but once you try to rev it up, it pretty much stalls most of the time, and it also won't idle down most of the time either, like the "fast idle" is not letting go. It acts like its bogging down whenever I try to rev it up. Anyone here who can help?