Biohazard

Seems to be working. Like I said; stone cold, she starts instantly and fast-idles for 30-40 seconds. Then the gagging (best description I have) which leads to stall.

It was running great - no issues but I let it sit since last December so, when I tried to reignite, and it was doing this crap, I first suspected varnish in the fuel way.
But after tearing down and cleaning the carb, I can rule that out.

Could this be vacuum?