Hi, I have just inherited a Rover Mower with a Briggs Stratton craftsman series II engine. Model 92508. The problem exhibited is that the mower will start but you cannot push throttle to full or the mower stalls.. If you let it run at half speed for a few minutes, white smoke starts coming out of the muffler...smells like burning oil. I have checked spark plug and cleaned the inside of the throttle body .also cleaned the air filter have also adjusted the fuel mix screw to full clockwise and the 1.5 turns anti clockwise... If i try and cut the lawn at this speed the mower just slows and stops if there is even a small amount of grass to cut. Thanks.