Norman, I think the only reason 2 strokes are still popular in karting is because some race classes are for purely 2 stroke machines, if it was all open class racing the four strokes would dominate, if you get the chance to look at a biland SA250 motor you will see its a peice of four stroke art, I manage to get some time in one, at the time I was racing long track karts, my kart had a cr500 2 stroke engine wich was quick, but the useable power the billand put out was staggaring, the measure of a good engine is not its HP but its tourqe, I think its only a matter of time before 4 stroke engines become the norm in paramotoring as the have done in so many other areas, quads, dirtbikes, superbikes, snowmobiles etc.
I think as the sport grows and more investment is put into it we will see some exciting developments in both types of motor, but I have seen this type of thing before and it only ever goes one way, a few companies will start to develope their own 4 stroke motor or will use a outsourced motor and everyone will start to follow, more investment and focus will be put on making the four stroke lighter and more suited to paramotors gradually the 2 stroke will fall from grace and we will all be flying more often with less problems, records will be broken for distance, height etc and we will all sit around a cold beer after a days flying and saying things like "I cant believe we actually flew a paramotor with a solo 210, blimey those were the days "