Are you using an electric starter? Or are you flipping the prop with a stick? Without an electric starter, most glow engines are tricky to start.

Put some fuel tubing on the inlet nipple of the carb and blow into it. If the needle valves are set about right, there should be a little air flow (you can hear it) when the throttle is at the idle position (barely open). There should be a lot of air flow when the throttle is open. This test will tell you if the fuel passge in the carb is blocked by dirt or gunk.