Briggs and Stratton?

I have been given an older Briggs and Stratton (5) HP motor. L head horizontal crank shaft.
I have completed a good fuel system cleaning and rebuild including tank and carburetor. New plug and oil change and the old motor cranked right up.
Problem is that it will not run up off of idle.
The carburetor is a fixed main jet model with no high speed adjustment.
It has the indication that the engine goes way rich when the throttle is advanced.
Can you give me some ideas on what to check to correct this condition?