The idling up & down condition cleared up when you partially choked the engine. This indicates a lean fuel air mixture. If the original carburetor was equipped with an idle mixture adjustment, the most likely solution would have been to open the adjustment to allow more fuel flow.

After installing a new carburetor, things went downhill. i suspect you overlooked somthing or did not connect the throttle linkage correctly and did not adjust the governed idle. The idle set screw may need adjusting. I do not suspect an internal governor problem.

My new carb is none adjustable. If I hold the govnernor arm with my finger clockwise, it runs great, a perfect idle. When I let go of it it races at max and the throttle does nothing to control it. I know that when the engine is off the throttle plate is held open then when the engine starts the plate closes on a correct running engine. I think when the engine starts the internal governor gear closes the plate when it starts but that is not happing on my engine.