I will tell you after fighting with one of these engines for a couple of months off and on that if the carb is set right (simple to do, actually) and there aren't any air leaks, the engine will idle smoothly and transition quickly. I can slam the throttle from a 1 minute idle and be at full RPM in 2-3 seconds. With mine, once the air leaks were fixed, I set the high end just off peak, and then set the low end to idle well and then to transition right. The low end is very sensitive on these engines when it gets close, so once you get it to idle for more than 10 seconds make the tiniest movements to dial it in.