premix is 40:1 with Mobile racing 2t and 91 pump gas. I cant really get a grasp on the smell. When I had my rh crank seal go out on my 96 RM250 it was very obvious, smoke was blue/black practically. This isn't white or blue and I really cant tell what the smell is. I think it may be the exhaust flange on the front of the motor isn't sealed up properly. As for the power, its kind of jumpy when in lower RPM's, jetting along with a few other things are getting looked at tomorrow when I wake up so it will be the deciding factor if the side case has to come off for a new seal, which the seal in there is new. There isn't any type of tracer you can add to the gear oil that would make it burn a certain color out the exhaust for proof of RH seal leak? That would be great but I doubt there is.