dual point distributor

So I have this dual point dist. from my 65 formula s that shuts off the motor as soon as I hook any vacumm to it. It has been rebuilt and the vac diaphram is in good shape. I even made sure it has the spring in the vac housing. what is going on? I have since switched to electronic ignition, but I have another 65 that I was thinking of putting this in. Anybody have experience with these things?
Dan