The Stovebolt Site Forums The Shop Area Engine Shop 1950 3100 - 261 Gas mileage?

Tuning to the original specs is IMHO just a starting point to get her running - it doesn't mean you are set for the best mpg/performance.

For example: today's fuel is totally different from what it was back than (it's way less volatile today), so it need's more advance to get max fuel economy, but it also can tolerate more advance before it starts pinging.
Personally I prefer manifold over ported vacuum, when it comes to mpg - idling, starting and temperature also benefit big time from manifold vacuum.

Also, setting your dizzy with a timing light under no load in your garage, does only work for idling. For every other rpm, it will not be optimal.
Since your mechanical advance is fixed to your rpm, there is actually only one rpm where you can set it to optimal timing (and that only under a certain given load).
Let's say you ether have an old worn out engine, or a hopped up one with a ton of speed parts - there is only so much you can do with changing weights, springs, and vacuum canister.
The only way you can tailor a curve that really fit's you engine is IMHO a full programmable dizzy.