I do not think this is a blocked vent issue after only 4 miles. I see clues however: new fuel lines, runs ok for 4 miles.
I would be checking for debris under the carb needle & seats causing flooding. A rich mix mixture for a cold engine might explain why it runs ok for 4 miles, but is then too rich once warmed up & then stalls. Pumping the pedal when hot is adding more air, enough to maintain combustion.