Too much or too little choke
Petcock turned off
Bad spark plug or plug wire
Bad seal at carb
Dirt in Carb
Clog in fuel line
Too much or too little throttle while starting
Gas tank not vented properly
Needle (spring) in carb not lifting
hook spark plug onto coil/plug wire and hold plug against side of head,pull the starter and see if you get any spark if so then that rules out spark. If spark is good try spraying a little bit of carb clean down throat of carb,twist throttle wide open with choke open and try to start if it starts then shuts off you probably have blockage in your carb possible main jet plugged with dirt. best I can do to help good luck!
In the hot weather my bike will only start with the choke completely OFF. When I firtst got my bike I must have spent an hour trying to get it going with the choke on. Tried it with no choke and it started on the first pull.