When folks bring in a trimmer that has sat all winter, I usually try dumping out all of the fuel, pumping the primer bulb to get rid of that crap too, then refilling with fresh fuel, back out the mixture screws an extra turn or so, fire it up and let it run real rich for a bit, dissolve all of that scummy varnish, then readjust. Half of the time that is all you need to do.