Correct jetting is way leaner than most people think. In actuality correct jetting isn't lean at all and what most people think is correct is WAY too rich. Bikes run pretty good way too rich except for making less hp, less mileage, and more carbon. I jet my mains like you jet your idle: just rich of stumbling. You can gain numerous hp doing that compared to many stock jetting setups. Nevertheless, idle and to a lesser degree midrange most always needs to be jetted a bit richer than optimum. Why the sacrifice? It's in order to better deal with the HUGE differences in vacuum and venturi size from cracking the throttle open. That a bit rich sacrifice is mostly to get through that just off idle lean spot that results from the big vacuum drop from opening the throttle. Starting that massive transition a bit on the rich side helps get through the lean times. Nevertheless, there is no need to go over board. More than just enough is too much!