Gasoline additive for carb messed up from sitting?

Drain whatever fuel is in it and put some fresh stuff in it. If you can access the carb see if there is a drain screw on the bottom of the carb bowl, (Honda's usually have a carb drain but not always) drain whats left in the carb until fresh fuel comes out. It should start once there's fresh fuel in the carb. With today's gas you cant leave an engine sit for more than 6 months without the fuel going stale, it wouldn't be a bad idea start the thing up every 2 or 3 months just to keep the fuel in the carb from going stale, plus when the situation arises when you do need it, she'll start right up for you.