The engine does not surge on the ground at all. When I bring the throttle back, the engine responds normally, and actually has an idle that is nearly perfect. The midrange is very good considering it is a DF engine. (i have flown fans before) The wierd part is that when I throttle back on the ground then go back to WOT, it will not get back on the pipe, unless I either pinch the line, or lean the needle. It unloads a HUGE amount in the air. I have to launch(its on a whiplash) with the engine well below peak, if not it will go lean in the air. It is just difficult to find the right needle setting to launch to get max performance without going lean. This past sunday I launched too rich, and the motor actually ran out of air to feed the fuel, and started 'missing' at high throttle. It would quit from flooding, kinda wierd for our engines.