New coil didn't do it

The next time you have to get another coil, get one that is labelled with "External Resistor Not Required" on the outside of the can. Those have a 3 ohm resistive wiring for the primary coil. That will limit the coil amps to about 4 amps and prevent premature burnout of the points.

There are 4 common runtime issues with the squarecan frontmount distributor

1) runs for about 1 minute and quits; bad condenser; not your stated problem
2) runs for about 5 minutes and quits; clogged carb filters; not your stated problem
3) runs for about 1 hour and quits; restarts after cooling overnite; bad ignition coil
not your stated problem
4) runs for about 15 minutes and quits; restarts after a couple of hours
sound like your stated problem?
BAD IGNITION SWITCH $10 (cheap)..... ...Dell

When it"s warmed up (15~20 minutes)it should run a little better on a lean condition. Not sure if we are talking at idle or not here but something is either blocking fuel flow or increasing airflow downstream of the carb. It"s entirely possible that there is a maniflod leak that is opening up as the engine warms. Dell had a good suggestion the other day to take WD-40 and spray around the intake manifold while she"s sputtering and see if it suddenly smooths out. Wherever that spot is would be where you are losing vaccuum.

The other thing that comes to mind here is clogged fuel filters. Check and clean out all 3 of them. There is a possibility that the tank vent is plugged and an easy way to check that would be to loosen the gas cap when it starts running rough.

So far as the new ignition parts, hey you probably needed them anyway. The 8 volt battery should go if it will start on a 6V. I had an 8V in my 2n when I got it and it fried the coil. Not sure if that"s the culprit but I feel good blaming it. The engine turns slower on 6V and doesn"t start as easily but it will fire eventually.

Hope these thoughts help