THE CARBURETOR SHOP / Fuel valves

The Carburetor Shop LLC

204 East 15^th Street

Eldon, Missouri 65026

Carburetor fuel valves (a.k.a. needle and seat assembly)

There are a number of different designs of fuel valves that the enthusiast will encounter when working on carburetors. This article will describe the ones most commonly found in older vehicles.

Conventional pointed valve with brass seat

This valve is the valve of choice for virtually all original applications. There are a number of variations of the valve: monel steel tipped solid valve, monel steel tipped valve with spring and plunger, neoprene tipped solid valve, neoprene tipped valve with spring and plunger, plastic solid valve, and brass or monel steel solid valve, with neoprene washer encapsulated in the seat.

One may find lots of posts on various internet forums concerning the neoprene tip. Many have had issues with the neoprene tipped valves, and immediately determine (erroneously) that the neoprene tipped valve is not compatible with the current blends of fuel. Our testing has not found this to be an issue. However, many NEWER neoprene tipped fuel valves do fail prematurely. It is our opinion the reason for this premature failure is due to the valve manufacturers eliminating the “staking” procedure from the manufacture of the fuel valve seat to allow the valves to be sold cheaper. Staking was simply driving a hardened pointed tool against the broached orifice of the seat. This procedure would eliminate any sharp edges created with the broaching procedure, and create a chamfer that would give the valve a greater seating area. The sharp edges can cut into the neoprene tip, thus causing premature failure. The enthusiast can approximate this procedure prior to installing the new fuel valve in the carburetor. To do so, the enthusiast should assemble a block of wood, a steel ball approximately 1 ½ times the diameter of the seat orifice, a steel drift punch, and a ball peen hammer. Place the threaded end of the seat on the wood block (this prevents thread damage), place the ball inside the seat where the valve would normally fit, place the drift punch on top of the ball, and strike the drift punch with the hammer. CAUTION – use the ball only once.

The spring-loaded valves were developed in the 1930’s (I think by Carter) for use on carburetors designed for off-road or marine applications. The spring minimizes the movement of the float during severe service, and maintains a more constant fuel level in the bowl.

Carter tried a thermoplastic valve back in the 1930’s, as the alcohol being used (yes Virginia, ethanol has been tried and rejected several times as a fuel; each generation has to prove to itself the problems of ethanol) would corrode the monel steel valves. The thermoplastic was impervious to the ethanol, but the point of the valve wore prematurely.

Carter also tried a solid valve made from either brass or monel steel that pressed against a neoprene washer encapsulated in the seat. These valves didn’t last long in production, but I do not know why.

Parker Brothers valve

The Parker Brothers valve consisted of an aluminum plunger with a concave trapezoidal shaped opening on the end facing the seat. A trapezoidal shaped neoprene disk was inserted into the concave opening. The trapezoidal valve would stay in the trapezoidal opening’ The seat orifice was surrounded by an inverted flare. The flat lower portion of the trapezoid sealed against the inverted flare. These valves had the benefit of much more consistent bowl levels, as full flow was available whenever the valve was off the flare (no point in the orifice). Also, as the plunger was produced from aluminum, it could not be magnetized. Unfortunately, these valves are no longer in production.

The “Wafer” valve

The wafer valve was similar to the Parker valve in design (the seat was identical); however, the valve was solid aluminum. The sealing action was done by a neoprene disc encapsulated in a small hex-sided wafer. The wafer was inserted between the seat and the valve. If this valve is used, IT IS IMPERATIVE that the rebuilder pay close attention to the float drop setting. We have had carburetors sent to us for rebuilding in which the wafer had turned 90 degrees, and was holding the float open continuously. We do not use this valve in our shop.

The “2-ball” valve

This valve was constructed as an encapsulated valve that used 2 glass balls of different diameters. The large diameter valve closed the orifice, and the small diameter valve was located between the large valve and the float tang. Our testing found these valves to have considerable less fuel flow than other valves, plus we observed valves that would stick in the open position if allowed to completely dry (enthusiast vehicles sometimes are not driven as often as they might be). We do not use this valve in our shop.

Summary

Other designs have been used in some specialty carburetors, but the ones described above are those one will most likely encounter. Regardless of the valve used, the enthusiast should remember that proper bowl fuel level is critical to the performance of the carburetor. Fuel level may be influenced by changing the fuel valve orifice from the specified diameter and also by the inlet fuel pressure. The trick is to use a valve with sufficient flow volume for the engine requirements, but not so large an orifice that the flow overbalances the buoyancy of the float.