It could be a bad starter, or a weak battery. It could also be be that your not getting enough heat to the plug. I spent 30 mins trying to start my motor one day only to realize that my remote glow heater was getting a little weak. Try powering your glowplug off your power panel and see if that helps get it running. Here is a pic of the 20 C carb. If your high end needle is shorter than that, you have the bad carb.