[30 Closed Cab PU]

Had slightly poor running, would not idle down smoothly. Spent weeks fiddling with the Carb, electrical, and troubleshooting for intake and exhaust manifold leaks. Finally temporarily ran a metal dryer vent hose from the carb air intake to just behind the radiator and issue disappeared. Finally found a small leak (small enough there was no audible sound from it) where the exhaust manifold was clamped to the muffler. Fixed leak - issue solved. Best guess is exhaust gas was getting into the carb air intake.