72 slant 6 plymouth duster will not stay running

My guess it's a fuel pressure problem as the choke is creating a vacuum sucking up the fuel instead of the pump pressurising and feeding the carby.
Another trick you can try.
1/ take off fuel cap
2/ disconnect rubber hose from fuel line running to carb at tank.
3/ put air gun to hose and blow air into tank.
You should here bubbling in the tank. If so its not the strainer.
4/ if it is the strainer will go thump as its blown of the end of the pick up that will fix the problem.
5/ pull out the tank and fish out strainer to clean and put back on or leave it in the tank an get another strainer it won't hirt anything laying in the tank.