2 cycle weed trimmer dies after running on full throttle?

I have a new poulan pro weed trimmer with a 2 cycle engine. When i run the engine full throttle, its fine. But when i let off the gas, the engine stalls. But if i slowly let off the gas and touch the gas a few times before it stalls, it idles fine. Is this because its a new motor? Or do i need to tweak the carb?