i had a theory about the solo 210 installation, and after seeing your pictures it might still hold true:
the solo is used mainly in a pusher configuration - there isn't a high speed flow of air in the vicinity of the carb as such. with the tractor configuration, there is a blast of air that goes right by the carb.
on the 185, it uses a velocity stack (or trumpet for bike folks) with a bell mouth at the end (flared almost to a flange). in fluid dynamics, this bell mouth means that if you put a jet of air over the opening, it would NOT act like a spray bottle and create a vacuum inside the trumpet - it provides a neutral pressure zone at the opening as if there was no flow there at all.
everyone knows that if you are drinking a fountain pop out of a cup with a straw, and you blow over the end of the straw horizontally, that the pop will rise up in the straw due to the suction that the airflow creates inside the straw.
well, with these solo 210's and having just a carb filter over the intake of the carb instead of a bell mouth opening, and the prop blast going right over the carb, i'll bet that the prop blast is interfering with the normal pressures the carb is used to on the intake in the tractor configuration. i haven't seen one other solo (or rotax 185) installation that uses this engine in the tractor configuration. and if there was one, i'll bet the carb is faired from the prop blast somehow.
on daffy's solo's, his carb filter is soaked with gas on the backside of the filter but is dry on the front side.
its just a theory, but like always i'm full of them. to see if it makes a difference, perhaps place a fairing over the carb on the front side, or some kind of air filter housing like on a car that would ram the prop blast into the carb for a "boost"
Tyler