Here's something I learned from much experience with Tecumseh float valves having the soft seat and metal needle:
Tecumseh always recommended installing the soft seat with the sharp edge of the seat going into the carb body first. ...This left the tapered opening facing the point of the metal needle.
The tapered point of the needle would wedge in the tapered portion of the seat, causing the needle to stick closed.
After fighting this on many occasions, I began installing the soft seats in the opposite direction, so the tapered portion went into the carb body first.
The point of the needle now makes a "line" contact against the soft seat, which seals, but does not wedge together.
Do not use a screwdriver to push the seat into place, as it will damage the seat. ....I used a B&S fiber point plunger or a cut-off B&S air cleaner screw, but any flat-bottomed rod of the correct diameter will properly install the seat.
This method served me well for many years in our shop. ...I hope it works for you, too!
Edited by Bruce Dorsi, August 11, 2017 - 07:25 AM.