Burned a valve -- now what??

if you burnt a valve, likely lapping wont help, you will have to replace it. valve lapping is used these days for getting the valves and the seats to seal right away after a valve job, or for freshening the seal on race engines in the field. basically you disassemble the head, and using a lapping compound and a lapping tool, you rotate the valve back and forth on the seat for a few seconds, rotate the valve 90 degrees and repeat. you should have a thin line on the valve and the seat indicating where the valve and seeat contact each other. this line needs to be consistant in width, and location. remember to remove the lapping compound from the seat and valve as thoroughly as possible as the lapping compound is an abrasive.