The Holley 1940 carburetor uses a Nitropyl type of float and because they tend to absorb fuel over time, we recommend that they be replaced at each carburetor rebuild. Once a Nitrophyl float has absorbed fuel it will become too heavy and allow more fuel to enter the bowl than what is needed, causing a flooding effect.The Nitrophyl float can be identified by the black color and it looks like it is made of a plastic material. The Nitrophyl float can only be tested by weighing it with a gram scale (14.5 grams). We now have the brass replacement floats for the Holley 1940.
To test the brass float: Heat up a pan of water just prior to boiling. Immerse the float and watch for any bubbles coming out of the pontoons. The heated water will cause the air inside the pontoons to expand and any holes will show up as bubbles.