Our engines can and will start and run backwards. The most common cause of this the engine is over-primed, basically has too much fuel in it. The best way to prime your engine is without the glow driver in place open the throttle fully, cover the carb mouth (or the end of the muffler), and turn the engine over by hand. When you see the fuel enter into to carb turn the engine over 1-3 more times. Then close the throttle and try to start the engine. If it still runs backwards then you are still priming too much, so simply reduce the number of turns when fuel enters the carb.

Ken