I just bought my Lawnboy used. It's a 20" cut about 10 years old I would guess. It's having a hard time starting, and runs not too bad for the first ten seconds. But then after that, it starts to rev, like you wanna race the guy next to you. If I look under the top cover at the front of the engine, I can see a rod with a spring wrapped around it. At the end of the rod, is attached another rod that goes straight up. As it revs up, then down over and over again, this rod is moving up and down, in sync with the reving. I imagine this is attached somehow between the governor and carbuerator? Any ideas what could be wrong and how to fix it? Thanks in advance!!!