How does the inside of your tailpipe look?

Do you do a lot of highway driving?

Unless my tailpipe and plugs look rich, I like my car to run a bit rich so that it does not lean out on the highway.

It wouldn't surprise me to turn a flat or two on HS6 carbs..

The human "smell test" seems very difficult to quantify to me. You may have a very sensitive nose, but I usually stick to the recommendations given in repair manuals.

Michael;

I definitely find improved Winter to Summer running by varying the Jet Adjustment Nut two flats (obviously leaner in the Summer). See: http://www.sw-em.com/checkchoke.htm#seasonal_adjustments

Cheers

Google says 59º for current temp but whatever. Would be interesting to know how many flats down you have currently set on both carbs. They won't necessarily be the same if they've been critically set. Base setting normally 12 flats down but that usually ends up a little bit rich. Might end up being 10 and 11 front back or reversed. SU's with worn throttle spindles hard to tune. Correct needles for your engine spec needed and these too shouldn't be worn. Clogged up air filters will also richen things up. Start with checking the valve clearances, then points/timing, before carb adjustment.

Yes, HS6's need a flat or two between summer and winter, HIF6's have it built in to some degree via bimetalic strip. Stick a new set of plugs in it and read them is the best way to go.

How can you smell it rich while driving around? Is your exhaust leaking into your cabin?

Fuel: there is no room to change the btu's of fuel, it mostly revolves around trying to make it easier to start in winter, however, do your best to avoid gasoline with oxygenates.