Is this a rebuilt motor? If you have fuel and spark, it is more than likely a timing issue. Dist. could be out 180. If it' s in correctly, it should be atleast trying to catch or backfire through the carb. Did you replace the timing chain, and if so, was it installed correctly. Only other thing I can think of would be an overly tight valve adjustment. And good point by Drew, "counter-clockwise", right.