There's a whole Engines Discussion group here on RCU. That's where you should post this type of stuff...

What's your procedure for starting the engine? Are you like many/most people, just plug the glow ignitor on and crank crank crank crank crank crank crank away with the electric starter? You're making an easy task very difficult, and wearing the engine out at the same time.

You have to prime the engine every time you start it. First, open the throttle to full, and place your thumb over the carburetor. Turn the engine over slowly by hand until all the bubbles are worked out of the fuel line, then turn the engine over three more times. Close the carburetor to idle, and turn the engine over three more times. Apply the glow ignitor and bump the engine with the starter. If the engine is already properly adjusted, it should fire right up.

You may be having trouble keeping fuel in the fuel line. If the fuel just drops back into the tank every time you turn the engine over, you have a bad air leak in your fuel system. There is no way to visually check your fuel system; even if it "looks fine" there may be invisible pinholes in the lines or a bad connection somewhere.