spitfire ignition timing

[trunnell@mindspring.com (Glenn Trunnell)]

Hello listers,

I'm wondering if anyone has any experience with advancing the timing on a
'76 Spitfire.  The manual and the sticker say that the timing should be set
at 2 degrees ATDC.  My car will run when set to this but runs much better
when the timing is set to about 8-10 degrees BTDC.  Is this just an
emissions lowering trick or is there so much advance (centrifugal and
vacuum) in the distributor that it is really necessary to retard the timing
this much?

Thanks in advance!