Take valve cover off dead side and see if push rods are still in place, go on youtube and type in how to adjust valves on Briggs and Stratten, if push rods are off you need to pull them out and make sure not damaged, put on flat surface and roll to see if out of round (if so replace) make sure you see which push rod goes where they need to go back in same spot, if in place adjust both cylinders valves, if still dead take out spark plugs on both sides put your thumb over dead cylinder spark plug hole spin engine with starter it should blow your thumb off if it doesn't you have a deeper problem. tell us what you find.