RE: Lapping valves on 4 stroke
I have used auto rubbing compound. What I do is apply the paste and drop in the valve. Then I use a small piece of silicon fuel tubing and push it over the valve stem. holding the tubing between my fingers and slightly pulling on it, spin it back and forth. Don't over do it. It doesn't take much to reseat them. What ever you use to lap them, make sure you clean them real good afterwords before reassembly. Be sure to clean the valves and seats well before you lap them. Sometimes all that is preventing a good seat is a bit of carbon or crud.