318 has developed a miss?

It cannot. The popping out of the carburetor is the cylinder still firing. It cannot fire if the intake valve is burned, because that cylinder cannot build compression. However, if the exhaust valve is closed for whatever reason, bad lobe, bad lifter, bent pushrod, broken rocker, or a combination, the cylinder will still fire, but the exhaust will be routed back through the intake and out the carburetor. Disagree all you want, but that's how it works. I suppose if the intake valve is burned, it's possible to get a pop, but nothing like what I am talking about. when an exhaust valve is held closed through the exhaust stroke due to damage, the pop will be LOUD and rhythmic because it will be happening every single time that cylinder fires. You will not have a "skip" as defined by a dead cylinder, but it will run like hell, because exhaust is being routed where it does not belong.

I am not saying that's what his problem is. I am simply describing what happens when an exhaust valve doesn't open.

Your talking a backfire through the intake, and I thought we were talking about popping like a lean condition pop under a load.

Fuel burns weather it's under compression or not, just not near as sudden like when compressed.
So a burned intake valve can certainly cause intake popping, and a slow to close or hanging intake valve can do the same. (open or burned intake valve ignites the fuel in the intake when the plug fires)

A non opening exaust valve lets the burning fuel back into the intake doing pretty much the same thing, but with much more heat and pressure.

So I guess we don't know if it's pop or a POP! when the OP's car does it. :-)