Honda S90 Over-revving

I am having a problem with my Honda S90 over-revving when I start it. I have cleaned the carb, blown out all the jets, set the air screw properly, and made sure that I dont have any excess air coming into the carb from the inlet side. I have insured that the throttle valve is sitting at the bottom of the carb body in what should be an idle position. Has anyone had a problem like this and have a potential solution?