Distributor timing

[3261R]

I'm rebuilding a '72 +2S Federal with the Stromberg carbs.

The vacuum advance/retard diaphram is shot. The distributor is a 25D with the centifugal unit stamped "10" and both counter weight springs seem to be the same.
Where the difference comes in is that this is now a non-emission car that now has to run on unleaded fuel.

Has anyone out there found an improvement - in terms of performance or fuel economy - by altering the distributor curve (the dispatch #41225A) or vacuum unit code 2/4/3 (https://www.britishvacuumunit.com/lucas ... nit--.html) on non-emission stromberg cars that have to run on unleaded fuel?

The maintenance manual shows an extra 10 degrees advance for the 40953 (non emission) spec but no mention of a change in vacuum spec.

I see ( https://mgaguru.com/mgtech/ignition/pdf ... _specs.pdf ) the Cortina Twink used the same 25D4 dispatch #40930A but with a vacuum code 1/6/10.

Any thoughts?

[SENC]

I think most guidance is to go to the Euro spec, including eliminating the vacuum retard, which to my understanding only served to reduce emissions and add gas mileage at cruise. I had Distributor Doctor build up a new distributor from old stock bits to 40953 specs, and bought the bits needed to rebuild my old one to the same as a backup. Works well, along with elimination of the emissions additions to the fuel delivery system and a switch in needles.

[3261R]

Thanks for this, It is the direction I was heading.
I'm thinking more in terms of the lotus Cortina Twin Cam's use of 40930A and the 1/6/10 vacuum. It's a proven combination - assuming the basic engine configuration didn't change. And the 40930 is very close to the 40953 spec.
Do you remember what vacuum spec you used?
Jon.

[2cams70]

I would not trust that data. Certainly no English Lotus Cortinas had vacuum advance. I think only the Mk1 Lotus Cortina made it to the USA and I doubt even these would have had vacuum advance because they were made well before the applicable emission regulations came into force. They may have confused the Lotus Cortina with the pushrod engined GT.