[Sunnybrook Farm]

I would think it comes down to how one drives and also how the car is timed. If you read the Ford manual they are talking about normal speed driving at lever half down and only at high speed is it fully advanced. People drove differently 90 years ago and the manual says to shift to second at 8 mph and high at 15 and they never talk specific speeds when giving spark adjustment instructions. At that time the state wide speed limit in Virginia was 35mph. I have been driving A's since the early 70s and back then a lot of the old guys didn't wind out the first two gears, just got the car moving and got into high. Driving this way fits running with the spark 1/2 or so down then once in high advancing the spark. If you watch youtube videos of people driving, they really wind the lower gears out and are turning lots of RPMs so they probably need to be at advanced spark. I would retard the spark when going around a corner and not shift into 2nd then advance it once speed picked up again. So I say if you drive like 90 years ago then follow the manual but if you wind out the gears then advance the spark sooner. Keep in mind that Ford didn't use this system after the Model A and speeds increased, it is a hold over from driving Model T's in a way.