I have a 18 hp briggs twin, model 350777, type 1137-E, code 00012011 that runs rich above idle. I at one time ran some bad gas through it and it hasn't seemed to be right since. I drained all the gas out and have run nothing but alchol free since. I've mowed with it a couple of years since. It idles OK but loads up above idle. I've changed the fuel pump with a new oe one, changed the carburetor with a new oe one, and today changed the carb with a Amazon knock of with the same results. I'm not sure where to look next and hope this is something simple to fix but not sure where to look. anything above idle and it runs super rich. I'm open to suggestions.