Take apart, clean/soak in solvent, spray with brake clean, wash with soap and water, rinse, blow out all holes, etc. and dry thoroughly. Put the new stuff in. Level and drop per instructions. If it has drill passages that have been blocked off with plugs, skin them over with JB Weld or they will leak gas or suck air. Piece of cake. It will run like a new Briggs and Stratton. Why don't you drop in a V8? not that much more work
