Try feathering the throttle (gently pulsing the pedal). If that fixes it you probably need to look at your choke. (I've had several cars without chokes that I needed to feather to get going.) What it's doing is using the acceleration pump to enrich the mixture.

If that doesn't work either then maybe the acceleration pump isn't working. You can check that by opening the throttle while you're looking in the top, you should see a squirt of fuel in the primary barrel.