Vacuum retard on a 051 distributor?

[FresnoBob]

I'm challenged with rough running off idle, but smooth running once the rpms climb.  My dwell is exactly 38º and the timing, with vacuum attached is at 2º BTDC at idle, and 30º at 3,000 rpm.  When I remove the vacuum line to the distributor and plug the rubber hose connected to the intake manifold, the timing at idle jumps to 14º.  I thought the 051 distributors had a vacuum advance system, so I'm very puzzled.  What should the timing be with and without vacuum attached? 

[mrfatboy]

With everything attached set 38 BTDC degrees @ 3000rpm.  It should fall down to approximately 8 BTDC AT idle.

[FresnoBob]

I've tried that based on stickandrudderman's suggestion.  The car still didn't run well off idle.  Do you know what change you have at idle with and without vacuum?

[mrfatboy]

I'm at 8 BTDC at idle and if I disconnect the dist vacuum I believe it moves 10 degrees to 18 BTDC if memory serves.

Which makes sense since there should be 20 degrees mechanical and 10 degrees vacuum for a total of 30 degrees of advance.

[FresnoBob]

Well, I'm not sure what is different from the last time I tried 38º at 3,000 rpm, but now the car is running fantastically well.  No more hesitation when accelerating from 1,500 rpm. 

Thanks for your help!