Sounds like it's to rich on the low end needle. After idleing for a while the engine tends to load up with fuel in the crankcase, then when you open the throttle it's to rich. In order to tell, open the throttle slower so it doesnt quit. you'll see a lot of ex smoke and raw fuel coming out of the muffler. Lean it out a bit at a time about 1/8 of a turn till it will maintain an idle as long as you want without quiting.