I recently bought a 1972 Polaris colt 22 with a 295. It has been sitting for who knows how long. I cleaned the points and have good spark on both plugs and I am using an external gas tank. I also cleaned the carbs. I cannot get the thing to fire up. All it does is shoot fire balls out the exhaust which I have disconnected. It also appears to backfire out of the carbs. I think the timing is off but I am unsure of how to set it. Any ideas?