I don't know anything about MVVS, but it sounds to me like your ST is out of tune. ST engines require adjustment of both the low end and high end throughout the throttle range. The first thing that I would try is adjusting the low end needle just a little bit richer (1/26th to 1/8th turn) and then retune the high end. Work them back and forth and you should cure your problem. The key word here is; PATIENCE, PATIENCE, PATIENCE.

It is too bad that your fellow fliers at the field don't have the time to help you.

Regards,
doubledee