I have a self-propelled mountfield with an RV150 engine. The throttle governor assembly does not allow full throttle. It starts and runs fine between fast tickover and half revs. if I jerk the lever between low and high it revs better for a few minutes then reverts to fast crawl. Been like that since new. Looking at the assembly the throttle attached by a lik to the flap it appears not to move at all. It's nowhere near the screw "stop" with lever on full throttle. Choke is fine. I cannot figure out how this assembly works. The way the fine spring attached to the flap is fixed - I can't see how the throttle could open, it pulls the opposite way! I could take my old suffolk colt to bits, and put it back together. again no probs. Searched utube for vids but none of the setups resemble the Mfield RV150 type. Can someone explain the mechanism?