backfiring problem, loss of power.

All of a sudden, my engine started backfiring out of nowhere. I left it on idle for about 10 minutes, then when accelerating, it would backfire. It was only noticeable when accelerating and putting strain on the motor by accelerating in gear. In neutral, wasn't noticeable, though may have been there. Later, even on idle, it would knock a little, well, not knock, but you know, like one of the cylinders was misfiring occasionaly. I narrowed it down to the one cylinder it occurs on. When disconnecting the spark plug cable on that cylinder, it idles great, none of that sputtering, misfiring. Changed all spark plugs and spark plug cable while I was at it, nothing. Next on the list, I'm about to put a new distributor cap/rotor on. What do you guys think this could be? And hopefully not expensive to fix?

I suspect a broken distributer advance spring.

Let's think about things that cause backfiring through the carburetor. Basically, it is the fuel igniting when the intake vavle is open. So, my thoughts...

1. Spark plug is firing before the intake vavle closes. Causes: bad spark plug wires causing cross fire. Bad distributor cap/rotor. Wildly incorrect timing...did you recently adjust timing and forget to tighten retaining bolt?

2. Timing chain has jump a tooth or more.

3. Intake vavle is burned and not sealing upon closing.

4. Intake valve spring is broken. Would likely hear racket.

Since you said you narrowed it down to one cylinder, to me this takes timing out of the equation.

Let us know what you find...might consider doing a compression check on the suspect cylinder.