I know these old trucks don't seem to get the mileage that you would think - mine was getting about 14 mpg average. Long story short - my 1951 has the optional oil bath air cleaner. When I got the truck, it had a couple of rust holes in the bottom of the oil reservoir and was full of dirt.
I cleaned everything up, soldered up the holes, added some 40 wt. oil up to the fill line and reassembled. Truck ran just fine, but a little rich even with a factory rebuilt rochester on it.
A couple of weeks ago, I was looking at the air cleaner and noticed that the space between the two outside pieces where it takes in air wasn't even all the way around. Went from about 1/8" to 1/2". Disassembled the air cleaner and found that when tightening the wing nut on the top, I had pulled the bottom of the air cleaner up.
Straightened everything up so there is now an even gap of about 5/8" all the way around. Evidently it appreciated being able to take in enough air, my mileage has gone up to 17 mpg under the same driving conditions.
