Looks alike you have 2 questions. I don't have experience with that particular airframe but I do with YS.

1. The YS91 and YS110 are roughly the same size/weight. The YS120 and YS140 are the same size/weight (about 5oz heavier than the 91/110).

2. I suspect that the extra weight added with the smoke system is causing the flight differences. Adding more power won't make it fly right.
Smoke just isn't practical in very small airframes because of the weight. If you just needed a bit more power then the YS110 would be the choice.