The choke does immediately open at the beginning of the first crank attempt, briefly, and immediately closes, but opens and shuts throughout most of the first attempt. It has different patterns for subsequent attempts. This is good, to allow time for a good field flash to occur.
It's going to be a fuel supply problem.
And there are so many things that can cause this problem.
Loose screws on cork gaskets (fuel solenoid, and blank plate);
Diaphragm with a pinhole;
Loose union between plenum and demand reg;
Loose hose fittings on top of demand regulator;
Leaking diaphragm cover gasket;
Stuck valve in demand regulator;
Kinked gasket (sleeve) on intake pipe (usually only if previously disassembled);
Debris inside of mixer (ants, submersion);
All of this can be checked in 30 minutes. And unfortunately, telling you to call a technician is not the answer either. Because not all technicians are created equal.
A manometer is a must, and unfortunately I know technicians running around with no manometer. Call a big time dealer....ask for the guru. "The one that fixes everything he walks up on." Accept nothing less.
State your problem, not your diagnosis.