[Bob Carriere]

Idling / stalling...... why and what is a on way valve for.....

Sounds like you have another simple but tricky problem.

At least you know you have spark or it would not start/run.

Have you installed a vacuum gauge....? if not think of doing so even if only temporary....... reading off the guage will help you out.

You may have a leak in the intake manifold.... gauge will show a low reading.

Are you sure the vacuum advance at the bottom of the dizzy is working...?
To test..... disconnect at the carburator....fit a tight rubber hose on it.... and suck...... with a 3 foot hose you should be able to see the dizzy move slowly....... suck and hold it with your tongue..... if it moves and stays moved your OK.... if it slips back you have a leak or perforated diaphram.....

You are sure the timing is A OK..... TDC or 5 degree before...... and that has to be set with the vacuum advance disconnected and the open line to the carb plugged......

How is it idling.... nice and smooth..... no puffing from the exhaust pipe...
When out of gear...idling.... if you give it gas slowly will it rev up.....if you press the gas fast does it stall......?

Make sure your vacuum line is connected at the base of the carb or directly to the intake manifold. Is the wiper line sealed/plugged at the manifold?? What kind of carb are you using.....pics..?

You have suitable fuel filter before the carb..... have you tried running the truck with a one gallon tank gravity feed above the engine..... careful for fire..?

Shame you missed out on Santa's parade.......

Get back with more info....

Bob