I believe it is cast in. But Martyn Bratby has developed a way by machining out the old one and making a new one that is held in with a back nut and fiber washers. Personally I'd rather work with the original seat or find another float bowl.
A bit of patience and maybe some ingenuity and you can lap the needle in. Ron
As Ron says the body is caste over the brass needle seat, the washer and thin nut below the bowl are for show only. Many a person has heated up the bowl and smashed at the brass insert with no success. The modern bowls now have a pressed in seat that is easily changed. Martyn Bratby does sell a new seat and needle combination but you have to remove the old seat first. As you know the M20 and a lot of Norton bowls have a horizontal fuel banjo underneath so don't have the thin nut but are still caste over the seat as above.
Thank you both.
My issue is not so much with the condition of the seat but more swapping a good seat from a cracked bowl over to a good bowl with the wrong fitting.
