Find the "model type date" code. It will be stamped into the cowl, generally above the spark plug but sometimes can be in different positions, or on a plate attached to the cowl. From the numbers you will be able to tell the horsepower and if you put them into the Briggs website you will be able to find a service manual for the engine.
Sorry I had my physic powers license revolted so as Aussietrev said need model type and date code and then we may only give the Ft lb torque if a newer engine as Briggs is no longer doing the HP ratings.