What engine is it?

first thing. if the engine is getting fuel, air, and heat it should fire. are you getting any kind of kick?

if not something is off.

you said you checked the glow plug.. did you check it by pulling it out and heating it up to see if it gets a nice even glow?

also if the engine is flooding then you might have it rich. reset the needles to facotry settings (cant tell you what they are withough knowing the brand) pull the plug and crank it to blow out the excess fuel and try again.

try starting it without the air filter on. if the filter is dirty then it could be chokeing the carb. (also clean and re-oil the filter)

again some more info would help us out.