Sam, in my experience Briggs side valve engines always miss an occasional shot, particularly at idle or light load. This appears to be simply due to rather marginal scavenging, which is probably to be expected in a side valve engine with a high bore diameter to stroke ratio. However except at idle it should be occasional, not frequent. (At idle I'd expect a miss about once a second, and at full speed light load, probably one every 10 to 15 seconds.) If you are irritated by that, the only cure I can suggest is what I did: get rid of all of your Briggs engines and buy only OHV Hondas henceforth. If in decent condition they simply never miss a shot.
