Weedeater 16hp and Yardsman 15 hp Ohv

07/04/18 I have a 16 hp and a 15 hp Yardsman and Weedeater ohv that make eratic puff missing noise thru the carb. THe 15 hp all the time. The 16 hp. on and off. Each has these strange carbs with a square base with a square plastic gastet with holes in it. No air and gas adjustment but a cylinder with 2 wires coming off the bowl. All my other lawnmowers have round base carbs and run ok. I think this is the missing , not so mooth running problem. Anyone have an idea.
Thanks

Check the valve adjustment.

7/4/18 Is there a table on the internet for lawnmower valve clearance. I know 181/2 hp Briggs is 6 thousands. A lawnmower mechanic told me the 16 hp is 4 thousands. so maybe a 15 hp is 5 thousands. THanks