I'm assuming that you have tried your glow ignitor onthe plug outside of the engine and assured yourself of a good quality "glow"?

Have you taken a few drops of fuel and placed it directly into the open carb to prime the engine?

Although I don't like to do this on a regular basis. A small squirt of Ronsonol lighter fluid in the carb also works and it light off even better than standard fuel.

When turning over the motor (using elec starter) with the carb wide open, can you see a fuel spray in the carb?