You've just cut the grass, now its time to break out the weed eater, what ?... You say it want start ?... well here's a few tips to get right down to the root of that weed eater problem.
If your weed eaters not starting first check to make sure you haven't flooded it, this can be caused by over cranking it and pouring to much fuel into the engine. If flooded put choke in run position and pull cord to clear fuel from engine , you may have to pull it several times. If still not starting Make sure your fuel tank isn't empty. Also to make sure fuel is reaching carburetor, if not your fuel filter may be clogged.
If engine runs but doesn't idle properly your carburetor probably needs adjusting. Most weed eaters have an idle speed screw that can be used to make adjustments, turn screw clockwise until idle speed increases. If this is not the problem you may have a worn crankshaft seal in which case you may want to consult a repair shop.
If engine smokes excessively you have an incorrect fuel mixture, empty the tank and fill with correct fuel mixture. You could also have a dirty air filter, replace if dirty. Also again check carburetor adjustment.