Difficult cold start

I have stock slant 6 (valiant -64) and I Am having hard cold starts.
I have tried different methods, first "don't touch throttle pedal" as manual states, and then pumping pedal few times and then crank. It always needs very long crank. I think it starts best if I keep throttle pressed fully open. Still needs many and long cranks.

Choke works (plate closes and opens when engine warms up). Ignition timing is correct and new spark plugs. Engine runs great and idles well when warm.

Any suggestions? My guess is that old holley 1920, but would it benefit if I put repair kit on it?
It is not really cold now here in Finland, just about +10 degrees (celsius).