I cracked the top plate on the carby on my old 99wr400. I had it tig welded. You need to find a good welder because it is cast alloy and can be tricky to weld. When I tried buying a top plate from Yamaha they said I had to buy the whole carby also.Later I found out Suzuki have the part that I needed whitch is off a Drz400 because they run the same carby and they sell the carby parts seperatly. In your case I would try to weld and then retap the thread.