that is my question. it seems you would want consistent cylinder temps to ease the jetting chore. there have been 50 degree days where i have been on the gas running open fields (4and5th gear)for twenty min and whaaaaaa there is a fouled plug. the freaking cylinder is cold as ice and the radiator is cold too. the jetting is already lean. 168 from a stock 172 and 45 pilot from a 48. the motor likes the cold (dense) air. i dont think leaning it would be a good idea. seems the extra cold air from the speed is keeping the water in the radiator from coming up to temp. seems like a thermostat would be beneficial. i can get heat in the motor by blocking one of the radiators but this seems pretty low tech to me.