8 N Ford tractor

This has the characteristics of a bad coil, but if it runs indefinitely after you tow it to start, that's wierd. So, some general things to check that may or may not apply specifically in this case:

Check for spark when it quits and you try to restart it. Hold a plug wire bare end 1/4" from the block to see if it arcs a spark when cranking.

Check the little spring-thingy contact on the bottom of the coil.

Check the keyswitch by bypassing with a jumper wire.

Make sure ALL electrical connections are clean, tight and bright, including the terminals on the resistor block behind the dash.

Makes sure gas is flowing freely from the carb drain when you remove it. if not, check and clean the filters. Make sure the gas tank vent is open(check by loosening gas cap when trying to restart).

I think you are probably having a problem either with starving for fuel from some part of the fuel system being plugged or that you have a problem with ignition.

Remove the plug from the bottom of the carburetor and let the gas run for at least a full minute to assure that there is suffecient gas getting to the carburetor. If the gas reduces to a drip you have starvation of the fuel for some reason. Check all the filters and the one in the tank on the fuel cutoff valve as a last resort. They can plug up too.

It is also possible that there is crud blocking the high speed jet in the bottom of the carburetor. Even is you just finished doing a thourough cleaning of the carburetor it can be plugged again. Open the high speed needle a couple of turns and see if this helps. It is does it's a sure sign that you have crud in the bottom fo the carburetor plugging the high speed jet orifice.