Holley 1920 Leaking Diaphragm

A customer was asking me about the hole that is located on the bottom of the main body (bottom of the float bowl. See the illustration and notice the small hole next to the mounting flange. His carburetor is leaking through this hole and it shouldn't be.

This hole is the relief, or indicator hole coming from behind the accelerator pump diaphragm. What does fluid coming out of this hole indicate? 1. The diaphragm could be ruptured allowing gas to get behind the accelerator pump diaphragm. 2. The metering block that cover the diaphragm could be warped (so many of them are because of the way they are tightened down), allowing fluid to get past the block and into the dry area of the diaphragm socket. The solution to #1 is easy, rebuild the carburetor, replacing the diaphragm. While #2 isn't quite as easy, it isn't a big deal either. Use a flat faced grinder to grind it flat and if that isn't available, then use a good flat file and file it flat. As a last resort, you can apply a small amount of Permatex anaerobic gasket sealer around the edges of the diaphragm.

Now if you just rebuilt the carburetor and need to replace the diaphragm, then keep in mind that there are several different diaphragms available for the Holley 1920. The differences are the stem length, stem is flat, or round and the cutout pattern on the diaphragm gasket area.

When you tighten the block down, start from the middle and work your way out, tightening the screws a little at a time.