Buy a can of carb cleaner and a pair of safety glasses. Warm the engine up to full temperature, and maybe recruit an assistant to sit with his/her foot on the accelerator pedal to give it a boost if/when it bogs down. Then, with the lid off the airbox, give the carb a good hosing all over the top surface, and down the primary barrel (the one that has the choke flap at the top of it).
In case you're wondering about the safety glasses; carb cleaner bounced into eyeballs is extremely painful and potentially seriously damaging. Wonder how I know?
