I had that problem and it drove me nuts, too. Then I changed the packing in my silencers and found that one silencer had different packing than the other, even though I bought them new. After I changed it, it smokes the same out of both sides and runs soooo much better. Prolly not what's making your's do that, but thought I'd mention it.
also, When I bought my banshee new, I found out that the carbs were way out of tune. The floats were at 2 different hieghts, 1 airscrew was at 2 turns, and the other was at 1 1/4, and they were out of synch.