340 popping through carb at low RPM.

One more tip. Open the hood running at night. Look for arcing around the plugs and wires and at the cap. If it's an automatic, get someone to sit in it hold the brake hard and apply the parking brake. Drop it in drive and gently run the RPM up just a little to load it up some and look for arcs. Sometimes it takes a little load for it to show up.