The Holley 1940 will use a check ball and then a check weight in the main discharge. This combination is used to keep the discharge hole closed when it isn’t being used.
What if the check ball isn’t sealing? Look down the carburetor at idle, or right after turning off the engine. If you see gas dribbling out of the main discharge, then chances are the check ball is leaking
How do you fix the leaky check ball. Tap the ball with a drift punch lightly to form a good setting for the check ball.
Holley 1940 Check Weight
This is the Holley 1940 check weight. These are not produced and if you lose your check weight, then your choices are to find a donor carburetor, or make your own. This one is a bit harder than most because it is a hex shaped weight. I would say the most important spec is the weight. Too much weight and the check ball will not lift as it should.Here are the specifications. Brass 1 gram in weight 7/16″ long 5/32″ wide, point to point of the hex.
An alternative is to add 1 more check ball on top of the 1st check ball. This is not the preferred method, but will get you by.
The check ball required for the discharge is a steel 1/8″, part 90-21