A slightly burned exhaust valve will cause a rythmic popping noise at the exhaust pipe- - - - -a little bit of compression/combustion pressure escaping before the valve is supposed to open. A burned intake will produce a rough idle and fluctuating manifold vacuum due to pressure escaping into the intake manifold. A slightly burned valve is sort of like being "a little bit pregnant"- - - - -things aren't going to get better on their own! As valve burning progresses, the cylinder will lose compression and eventually develop a dead miss.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!