My Briggs and Stratton 10D902 lawnmower engine is running very rich. The air cleaner is OK
Can you please advise

Check to see if the choke is stuck in the closed position if not it could be a float in the carb has a hole init and overflowing the carb.good luck.

check to see if the choke is stuck in the closed position if not it could be a float in the carb has a hole init and overflowing the carb.good luck.
The carb does not have a float or a choke. The engine has a diaphragm type carb

Clean the carb, readjust, run some sea-foam, or berryman's b-12 through the fuel system.