
It is most commonly used to make the mating surfaces of intake and exhaust valves conform to the valve seat surface, to ensure a tight seal. Same thing you want for the sediment bowl. The technique involves radially rotating the two surfaces together many multiples of times to “wear” the surfaces to a perfect fit. Most times, a slightly abrasive compound is used to speed up the process. To lap the fuel valve, you would remove the bowl from the tank and disassemble the valve, removing the nut and any remaining packing. You may be able to do it with the bowl still attached to the tank. But, it would be easier if removed. At any rate, rotate the handle portion into the seat using a moderate amount of pressure. Then keeping doing that for about 500 times. If you don’t want to buy a container of lapping compound, any tartar control toothpaste will do. It has a fine abrasive in it. This is a good job to do while you’re watching TV.
