Rugerfly,

It sounds like you have the tank mounted too far below the level of the carb. The best position for the tank is to have the tank centerline slightly below the centerline of the carb. With a full tank, this will put a little pressure in the fuel line prior to start. With this set up, if you try to start ther engine with the tank below one half full, the fuel will drain back into the tank when there is no suction draw from the engine. Usually you can get the engine started this way, but you must have a good prime to allow the engine to run long enough to draw fuel back up the fuel line to the carb. It's always best to use a full tank to allow the fuel to flow naturally to the carb for starting. Hope this helps.

PMW