Ignition firing and distributor questions

[TKing]

I have an miss-firing cylinder or 2, but it's hard to tell with the normal idle stumbling and noise. I attempted to determine which cylinders are miss-firing at idle by connecting a timing light to each spark plug wire and observing the light as the illumination reflected off the valve cover. It seems I have at least 2 cylinders that don't fire (light dosen't illuminate at a standard beat) routinely. I have new spark plug wires and new MSD distributer cap and rotor. The same missing occured with the old wires and cap. Maybe this is normal?

The engine runs fine except occassionally after a couple of hard accellerations the engine will backfire on decelleration through the left exhaust pipe. I initally thought the timing moved, but it didn't. I have adjusted the timing anywhere between 12 to 15 degrees with the same results. The backfiring disappears after the engine has cooled.

I noticed I have about .020 to .030 (estimate) up and down play on the distibutor roto shaft - normal?

The engine is a stock FMS392 430hp which was recently rebuilt.

Thanks for your comments.

Tom