My truck starts and idles well. When trying to rev up, engine stumbles, misses and lopes like crazy.
Ive replace distributor cap, wires, points, condenser, set dwell, timing and idle mixture. All within specs. Idle timing and full advence also within spec. Purrs like a kitten at idle, accelerates (when very slowly working throttle) to a point then stops firing. Let of the gas and begins firing again, idling well.
When hitting accelerator hard will rev well then stumbles. When held at steady engine speed, it runs rough, popping and spitting, or lopes like hell.
Ive noticed when turning rotor button there's about 3/8 in of play. Ive removed the vac advance plate and notice a little stickiness. Also have notice that 1 of the mech advance springs had been replace, other appears to be original. I'm about to lubricate these and nylon pads Vac advance plate sits and slides on. I do not have a vacuum pump to check vac advance, but when sucking on vac line it moves, not fully, but does move a bit. No leaks found.
My question is:
How much play is acceptable and how easily should mech advance weights move?

As far as I know, this engine is not rebuilt.
I had a misfiring issue the last day I drove it, and was hard to start. I removed the cap to check the points and realized the carb had caught fire, inside the air filter housing. I quenched that and continued to check the points. The points were a little pitted so I cleaned them and regapped.