That plastic piece and the associated linkages go on the opposite side of the carb from where they are now. You may have to re remove the carb and tank to get it where it goes. There should be a small threaded hole close to the carb mounting screw. it has a screw with a 5/16 head with about a 1 inch shoulder.
i looked at an old photo i posted and see where its suppoed to go.. at the bottom of the fuel tank there is a spring. do you happen to know where its supposed to go?