Yardman Riding Mower Won't Start?

My Yardman riding mower with a 20 horse Briggs cranks, but will not start. It has good spark to both spark plugs. Comp. check good/values adjustment checked, and fuel shut off OK. I tried starting fluid and was wondering if the coil gaps could be wrong. I would like to know what air gaps should be on the coil packs. Or am I missing something else?

By BH