No power from Cyl #3

[Bradley]

I do not seem to to be getting any power from cylinder #3. I have put a new rotor, cap, and plugs on. There is a spark comming from the plug and I have put my thumb over the spark plug hole while cranking. There seems to be the same amount of compression in all the cylinders, enough to blow my thumb off the hole. The plug in #3 when pulled is black and sooty. All other plugs are a tosty yellow/brown. There is also a clatter or Clacking noise comming from the engine. I can still get over 5 kts at 2,000 RPM, but the #3 is not fireing. I pull the plug wires while under way, and each cylinder has a big drop in RPM except for the #3 where there is no change in tempo at all. So what do we have here? Valve? How hard is this for a novice?

Thanks,
Bradley