Yesterday I was called by a buddy with a very bad surging issue at low speed, he has a 10 year old Honda a pretty big rubber track job. We went through every last thing, cleaned the carb reset the governor. THe setup for the governor was wrong in the manual but that was easily figured out! We were still scratching our heads when I thought of the one thing we din not check idle speed, it was bouncing so badly who would have thought!!!!!!!!!! Over time the plastic screw had worked its way out, a few turns of the screw driver and it purred like a kitten. As usual one cannot see the forest for the trees, I have been a mechanic for near 50 years and let something that simple get to me. Moral if your machine starts to surge check the idle first, all the governor sees is the speed getting to low and it responds by bouncing the RPM up and down.