Having some weird running issues with the Craftsman freebie.

Hi guys, we have had this freebie for a while now. We got through some issues with it not starting. Now after a carb swap is still does this. Acts like it will backfire and miss at slower speeds. Under load it is better. Acted like governor arm was stuck when we first got it to run. It will easily stall towards idle. Head gasket changed and valves adjusted to spec. Plug changed and spark checked for magneto health. Fuel pump is new and gas tank drained and refilled with fresh gas and sea-foam.
Any helpful hints we missed??????:dunno::dunno::dunno::dunno:
Thanks, here are two videos of it from today.