OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk carby leaking fuel - mechanically challenged :-)

If you look at the illustration above, you will see that the seat is a hollow cylinder: the seating takes place on the inner corner of its end-surface, so it should be a perfectly square corner (see just below the note 'press flush'). With normal wear a small conical surface would develop on that inner corner due to contact with the needle's conical sealing surface. The worn, conical part of the seat should be even all the way around. The simplest way to fix the leak would be to lap a clean conical surface, but if it were the least bit out of square, it wouldn't work. Similarly it must be quite narrow: the force applied to the needle by the float may not be enough to seal over a large area. I guess that is why B&S just say replace the seat. However if you damage that square inner corner of the seat the slightest bit while installing it, you've wrecked it. Hence the screw that goes through the inside of the old seat must be retracted so it does not protrude at all before you start pressing in the new one. It is the kind of job that is pretty easy for someone experienced, and pretty difficult for anyone else.

You said you've examined the conical sealing surface of the needle, and it is good. The slightest wear on that conical part of the needle has the same effect as wear on the seat. Unless it is pristine, replace both needle and seat at the same time.