[scicala]

To test it properly need to clean any dirt and make sure it's dry around the center hole for the air cleaner stud. Then seal both sides of the hole with a small piece of masking tape. I say this because the vacuum channel to the diaphragm passes through this area and is sealed by a brass bushing. The bushing sometimes doesn't seal well. This is why it's important to snug down the air cleaner stud to seal it once assembled again.
You can use your mouth to apply vacuum to the hole in the cover, then see if the diaphragm collapses and stays there. If any leaks (besides a bad diaphragm), it's usually because the diaphragm is pinched. Best to install it with the spring partly collapsed, as to keep the diaphragm flat when tightening the screws.


Sal