I have a Craftsman model 247.88957 with a ZS365-SUB engine. The engine surges at anything above almost full choke. I have dropped the float bowl and cleaned it out, pulled the float and blew carb cleaner up thru the jet. I have fresh gas in the tank with Seafoam. It still surges. I think it is running lean and needs a mixture adjustment. But I cannot for the life of me locate any mixture screw anywhere on the carb. I have pulled most of the shroud, turned it upside down, rooted around with a light and I see nothing that looks like a mixture adjustment screw. Please educate me. Where is it?