I tested spring lash in the ignition distributor by disconnecting vacuum advance, setting to TDC at idle, and at 3000 rpm's I'm seeing 25 BTDC.

So, with vacuum connected, I get 16BTDC and 40 BTDC at 3K rpm. The advance diaphragm under vacuum load is supposed to narrow the gap and allow 25BTDC under 3K rpms?

Assuming this is normal, is this something that the advance diaphragm regulates? There should only be 9 degrees difference in advance between idle and 3000 rpm.

David