New 47cc Pocket quad dies at WOT.. Help

Hi guys - I finally go the pocket Quad running and it will run idol for 30+ minutes no problem. I can also lift the rear tire up and let it rip full throttle with no problems (except a bit of white smoke from exaust). But if me or my son gets on it and ride it, it will die once the throttle is wide open for a few seconds.. Why does it only die when it has weight on it? Not enough gas (bad stock fuel filter)?? Thanks for the help!!