How so? Then everyone's got a timing problem! The engine runs fine. The Kohler on my old tractor used to backfire on shutdown with a much more pronounced bang if you didn't shutdown at 3/4 throttle. It's just unburnt fuel in the exhaust thanks to the ignition coil being shut off before the engine has stopped sucking fuel.
I don't find this a big deal. Sometimes it does this, other times it doesn't. I bet if you removed the exhaust pipe from the engine block it would never do it. The PT exhaust (in recent model 422/425's) has two 90 degree angles. I bet that increases back pressure quite nicely. If we could turn the engine 90 degrees or even 180 degrees counter clockwise we could eliminate one or two of those bends. Rounded corners would help. Perhaps custom headers are needed. /forums/images/graemlins/grin.gif
