Push mower wont stay running unless I hold air vane open for 45sec

Mower model - Troy-Bilt 12AV566N011
Briggs Stratton model - 126T02-0487-B1
Auto Choke

Problem:
Mower sputters after start and eventually shuts off. Found if i manually hold the air vane arm open for 45sec to 1min...everything warms up and the mower runs fine. I have to do this for every cold start.

What i did:
Replaced gasoline
Changed oil
Replaced spark plug
Cleaned carb
Replaced spring which controls air vane
Replaced thermostat (which pushes against the air vane to open)
Did not replace air vane itself because its just a piece of plastic and seems like in fine shape.

So the mower works fine after what I mentioned but quite a pain to hold that open after every start.

Any suggestions are appreciated
Thanks