vwq47, you didn't by any chance put the new seat in that Walbro LMS carburetor upside-down did you? If you have the version that has an all-metal needle, it uses a Viton seat. The seat has to be installed with the concentric circles upward toward the carburetor, not downward toward the needle. (There is also a less common version that has a Viton sealing area on the needle - that type uses a metal seat. If you replace both needle and seat as a pair all is good, but if you use a non-matching needle and seat, it may flood.)
