is it misfiring? because if it not misfiring it HAS NOT bent any valves?
this statement is not actually true, i have seen engines which have touched valves to pistons and they have bent them just enough to open up the valve clearences to make em tappety, but still let them run fine (albeit down on power)
get an engine stethascope and have a listen to it mate, you will soon find the area of noise
pugo