Re: First build done but have a question!
Make sure you're opening the choke - lever on the right side of the carb, should be in the down position. Either that, or the clutch cable is not adjusted properly; it should pedal without turning the engine over with the clutch handle pulled. Lastly, could be the idle is set too low. Rev it up standing still and screw the idle screw in a touch. I'm messing with my idle all the time.
In any case, it doesn't sound like a big deal. Welcome!