My throttle valve has a notch in one side and a groove on the other. I think the groove is supposed to fit over the bump in the carburetor while the notch fits over the idle screw. But the groove on mine is too narrow to fit over the bump.
Can I just file down the bump to get the valve seated all the way into the carb?
I had the same problem. By the time I realized it I had smashed the bump so flat that the throttle valve would not fit over it. I finally took a screwdriver and scraped the thing out. Don't ask me why it is made out of plastic and not metal. Throttle valve worked fine afterward. Got my spree up to about 33mph before I started having belt and clutch problems. Which is a whole other problem I am working on.
Incomel, you are absolutely right. I gouged out the sides of the notch with a screwdriver, so the valve worked smoothly. The thing started on the first kick and idled normally. Amazing!