I am getting a popping sound through the carb. It is still drivable but has lost some hp. I pulled the pass. valve cover and one of the exhaust valves lash was loose. Do you think a) collapsed lifter b) bad cam lobe c) about to blow up. I took out the pushrod and it looks fine. I have not turned the motor over to check any other valve lash yet. 454 86k miles. Opinions?

After tightening the lash did it appear to move as much as the other rockers, kinda sounds like a lobe going south.