Fuel and/or heat. If you've got a heat gun, shoot it at the head and the carb being careful not to get any plastic parts too hot. Or you can take the glow plug out, shot of fuel down the top, take the back plate off, shot of fuel in there, shot of fuel in the carb, open is best, but closed is ok, just let it soak in. Or you can just dump the whole thing in some fuel overnight. It'll free it right up and it'll be good as the day you left it.