My engine ia a 23 hp Briggs model no 445477 type0755B1. I have 325 hrs on it . it is using about 1 quart of oil in 2 hrs, blue smoke from exhaust. It has started to backfire especially at low speed, not as bad at high speed. I have changed the head gaskets and adjusted the valves ,new air filter , changed the oil an filter. nothing has helped so far. help.
