You need to choke the carb. The lever should be on the right side of the carb. Push it down and then push it forward a little bit to make it stay choked. Then if it runs, give it a little throttle to un-choke it.
Also, make sure your idle is adjusted right.
Take the right side cover off the swing arm, there should be a hole in the side near the carburator. There should be a brass screw sticking out of the carb. It's the idle speed adjustment. Turn that in to make it idle faster. The correct idle speed will make it run but not spin the back wheel when it's off the ground.
If that doesn't help, you may have a clogged idle circuit.
The fuel flow for idle flows on a different circuit (set of passages) from the main jet. If you look at the bottom of the carb with the bowl off, you should see one or two tiny passages into the body of the carb. Make sure those are clean.