AS far as mid-range is concerned, there is a carb jet that controls the midrange. If that jet is clogged, your midrange will suffer. I had one engine expert fix an engines mid range right there at the field using a techique where the engine was brought up to full speed, then the choke was applied fully, and just before the engine quit from the choke, the choke lever was then opened and the engine regained its full power. This was repeated four to five times, then flown. The engines midrange problem was then fixed. The guy told me that the back-flush of fuel will often times clean this jet without having to disassemble the carb and cleaning it. Be very careful during this procedure, Be sure the plane is held by another person and you can only do this safely if you have a choke extension which keeps your fingers well away from the propellor arc.