First of all make sure you are using proper starting Technic. Before you start cranking push the gas all the way pedal down to the floor, release the gas pedal then turn the key to the crank position. This does two things, Allow the choke to activate and put a squirt of gas in the engine.
You can check the operation of the choke when the engine is cold (not running or cranking) by removing the air cleaner and seeing if the choke valve is open or closed if it's open hit the gas and see if it closes. If not, spray choke cleaner on the linkage and see if that helps it close. The choke uses Bimetallic spring to close it, if the spring is broken, improperly adjusted, or restricted from moving the choke will not close.