Have 14.5 hp B&S engine and it runs smooth when idling. Give it full throttle and the govenor does not kick in just slightly in creases speed of engine. If you manually reach and pull the govenor lever and increase the speed of engine it will start to flow gas from the crank case tube that comes back to the carb. Also how do you syn the govenor with the throttle linkage.

There is probably too much friction in the linkage at the carb. Spray with carb cleaner until free.