I bought one of these units about a month ago, and its worked great so far. Love the power, but noticed that it smokes when first started. Is this normal? Ive only run the Stihl pre mixed gas that comes in the cans because I got twice the warranty by purchasing the pre mix 6 pack. Should I be concerned with the inital white smoke that comes out? its just a puff or so at start up, and quickly clears.