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Tech tip – Carter WCFB and Rochester 4-GC floats

One of the “gotcha’s” that often bites a novice carburetor rebuilder is float non-interchangability on Carter WCFB and Rochester 4-GC carburetors.

Both Carter and Rochester engineers determined that, on some applications, the float level in the primary side of the carburetor should be different than in the secondary side of the carburetor. Maximum float buoyancy is generally accomplished when the float pontoons are at a 90-degree angle to the fuel valve. To accomplish the maximum buoyancy AND have different levels, DIFFERENT FLOATS WERE OFTEN USED IN THE SAME CARBURETOR! Once, I checked the various Rochester floats that I had in my inventory, and at the time I had 19 DIFFERENT floats for 4-GC carburetors. I never counted the different Carter floats but there are more than a couple.

Now, tooling for different parts costs money, so one way different floats were made was to use the same arm, the same pontoons, AND SOLDER THE ARM TO THE PONTOONS AT A DIFFERENT HEIGHT!

Unless one is looking for this, the floats look to be identical, but when re-installing, one will find massive re-adjustment may be needed. Placing the different floats side-by-side will reveal the differences in height of the arms. This is NOT an error in manufacture; but by design. If the floats are interchanged, it may be possible to get a correct “static” setting, but the fuel level in the bowl may be incorrect as the buoyancy of the float may not shut off the fuel at the correct level.

Some of the Carter secondary floats have cutouts in the pontoons for the auxiliary airvalve, so these are quite obvious; but the ones with the same pontoons are not obvious unless one looks for them.

When rebuilding one of these carburetors, always nice to have the original bill-of-material for the carburetor to determine if the floats SHOULD be the same or different (one cannot count on a previous rebuilder knowing of this issue).

In the absence of the bill-of-material, one should pay attention to the height of the arm on each float, and if different, mark each float as either primary or secondary.