Mis-fireing back fireing problem

[gungadin]

This is a '76S with a '79 SC engine and points igintion.

I had this car tuned up and I put several hundred miles on it and it started to develop this problem.

Cold it runs smooth. As it warms up it developes a random misfire backfire and the hotter it gets the worse the problem.

It doesn't misfire if I put my foot into the accelerator hard but if I try to accelerate moderately or just maintain a speed it misfires.

When it is misfireing I can see the tachometer drop rpms instantly. The worse the misfireing the more rpms are not being displayed.

I just put new spark plugs and new plug wires in it but no change. The cap and rotor are new.

This problem coincides with a change in the weather as it has been raining quite a bit lately and I don't remember it doing this at all before the rains.
Although it wasn't raining this evening when I drove it just after the new plugs/wires.

Suggestions are welcomed and greatly appreciated

[billybek]

My 83 SC does a similar thing after a good long highway run. When speed is moderated and running about 2700 rpm the engine kind of fires against itself. Pulls like a freight train under acceleration though.
Watching this thread with interest...

[Paulporsche]

I would check the points/dwell angle first.

It's also posible it's your WUR/warm control pressure and/or mixture.

Make sure your plug wire ends are snapped on firmly. Also, new wires can be bad.

[tcar]

Read your other thread on this problem; about a coil.