What are the symptoms of a burnt valve or a valve needing to be replaced? Piston #3 does not fire when I run the engine...I pulled the heads off and the valves for that piston are black(new heads too) but the top of the piston looks clean as the day it was installed. Yet, when I run the motor I am getting no firing out of #3 the plugs are all new the dist is new and the motor just had an entire rebuild about 300mi ago. I did overheat the motor(long sad, stupid story, that I am embarrassed to talk about ) and originally thought that I had fouled a plug or burnt a piston, but they are all in perfect condition? So I am only left to assume that it would be the valves? Any suggestions.....BTW, the compression was fine when the motor was built.