When a large SuperTigre engine starts and runs backwards, it's because it's over-primed. Don't prime as much. You can also flip it backwards, which should help.

It's easy to over-prime the large 'Tigres, and they'll go backwards every time. Pinch off the fuel line and prop the engine until it's dry of fuel. Then carefully re-prime, but not as much. An electric starter will eliminate backwards starting. You can also try opening the throttle a little bit more, too.