How do I adjust the valves on a B&S 12.5 ohv engine?

You don't: there is no adjustment on the valves on any Briggs and stratton engine with overhead valves.
you have to replace them if they are lose.

Don't try to adjust them! Trust me I learned the hard way when I tried to adjust the valves on my 12.5 over head valve Briggs and stratton Engine. It ended up costing me fifty dollars to get the broken stud replacen in the head.

Mickey-G
July 2009

Reaching into the valve cover at the front, identify which valve is the inlet and which is the exhaust. Set the inlet clearance when the exhaust valve is just about to open, and set the exhaust clearance when the inlet has just fully closed. You can get the correct clearances from the B&S website but from memory I think the exhaust is .009" and the inlet .005".

John
July 2009