It sounds like you low end mixture is closed too much. Look at the manual and reset it to factory settings. I've set mine like this and it seems to work ok for starters. With the throttle closed completely turn the low end mixture screw (inside the throttle barrel) all the way in and then back it out 2 1/2 turns. That should get you close. Also set the high end needle about 1 1/2 turns out.

Also be sure you have a good glow plug. I'd try a new one just to be sure. Sometimes they will glow ok with the ignitor on but won't allow the engine to run.