<VV> LM ignition/distributor timing

[The Barneck's]

I am working on a 65 140.  the book says initial timing 18 BTDC, 22 degrees vacuum advance @14 HG, and 18 degrees @2800 RPM.

I have it set at 8 degrees initial timing.  I get 18 degrees advance at 2800 rpm.  I am getting the 4 degrees of centrifical advance at about 1200 rpm.

My problem it I get engine rattle when first starting out (which is why I retarded the timing to 8 degrees initial timing).  idle RPM looks to be about 900 (a little too fast).  The problem is when I hook up the vacuum advance line at idle, the timing jumps about 8-10 degrees in advance.  

Any ideas what I should be looking at?  what is causing the vacuum advance to work at idle?

Doug Barneck
back from the national convention and having to work on my son's corvair some more...