The C5 model was introduced in April 1941 to replace the F4, for use in RO and OD engines. The C8 model replaced the F6, for use in the larger QB and RQ engines. New features included a larger air valve and a cylindrical fuel strainer. Fairmont claimed that they increased horse-power, gave improved all-round performance and were easier to maintain. A C5 in my collection is shown below:
Metal Floats Replace Cork Ones
C5 and C8's were initially supplied with treated cork floats. However, cork will eventually absorb enough gasoline to impair its function. A move to metal floats in C5's and C8's was made as decribed in Fairmont Motor Car Performance Sheet No. 44, issued in May 1943.
From Aluminum to Plastic Poppet Valves
Plastic valves and valve seats replaced aluminum ones during the war. They worked so well that Fairmont never went back to aluminum. The article below is from Fairmont Motor Car Performance Sheet No. 61, issued in August 1946.
Carburetors for RK-A and RK-B Engines
The RK series engines have two cylinders. One carburetor feeds both cylinders with gas/oil/air mixture. To control this, there is a throttle butterfly in the body of the carburetor and one of the poppet valves is relocated to an adaptor that goes between the engine and carburetor. A diagram of one of these carbs from an M19-AA manual is shown below:
C5/C8 Carburetor Availability and Parts
Fairmont supported their products with a good parts service. The C5 carburetor service kit (part #51141) was popular. It contains all gaskets, valves, seats, springs and hinge pin. A complete gasket set (part #A1389) was available. Individual parts could also be purchased. In 1957, a complete C5 cost $38.60, a service kit $8.65 and a gasket set $1.00. By 1985, the price of a complete carburetor had risen to $251.65 and by the mid-90's was said to be $600. The last carburetor rebuild kits from Fairmont sold for about $110 in the mid-90's.
I doubt that Fairmont have any C5 or C8's left in stock. They still sell some carburetor parts but valves, valves seats and needles are long gone. Fortunately there are members within the hobby who do fabricate parts, including needles, valves and valve seats. Should you need a C5 or C8, there are quite a number of them in members hands. They have sold on eBay for between $50 to $150.
Last Edited 28 January, 2018