REJOICE, MY BROTHERS! WE ARE VICTORIOUS!
The issue was the new valve needle lever part from the rebuild kit. The pump/fuel intake would hold vacuum (so pump seal check valves ok), but NO pressure. If I took off the lever and spring and just held the needle down with my finger, it sealed perfectly. Put the old lever back on, 100% seal. Saw starts right up. For some reason, the new lever wasn’t allowing the needle to go down far enough to contact the seat.
Canceled the new carb, (saves me $90+) but I still got a new inlet pipe on order because one of the screw holes is stripped out. I suspect we still have an air leak there after the carb.
For anyone in the future reading this, the video below REALLY helped as well as all the help I received in this thread. THANKS GUYS!
Glad you got it sorted... Both youself & a bunch of others who read this down the track will be better off for your perseverance!
For what it's worth, a leaky main nozel (as a result of fuel line pressure) is pretty much always the metering system leaking. The nozzle check valve is only there to prevent back flow (from the venturi into the carb) & generally just causes tuning & running issues