The choke pull off only opens the choke so much (not all the way)
It is designed to open the choke just a little when the engine fires up.
The rest of it opening relies on the bimetal spring as the engine gets hotter, and sometimes they don't open all the way due to a plugged up crossover in the intake. (usually older OEM manifolds)
The other reason is that the bimetal spring that controls the choke is bad.
An electric choke conversion kit for that would be nice to have.