it retards (or advances) your spark for various grades of gasoline.. I just made that up, I've never even heard of one Paul
Sounds like the switch that picks what tank you're useing in a pickup with extra tank. Scouts had a switch to go from the left to right tank too.
NO! Seriously! I'm not quite strong enough to open the hood all the way by myself, (the hood springs are broke, I tried!). So here is a pic out of the service manual. This is the only place in the whol book they say anything about it. And all it is is an arrow on a picture. Honestly I am not making this up!!
Early GM, 1940's-50's? It's a timing adjustment, basically a screw with a thumb wheel and a degree scale allowing timing to be adjusted several degrees either way by someone with clean hands and no tools. It is intended to allow the car to be adjusted for varying grades of fuel and load. Basic drill is to have car's basic timing tuned to specification with the selector on its zero mark, then use the selector to tune out pinging by retarding or allow a bit more advance if car is happy with its diet.
Oh, okay. It funny how the shop manual dosn't say that. But maybe it does somewhere else? I havent read the whole thing, just the part about replacing the distributer. Thanks!!
Plus as an added bonus it makes farts smell like roses. You learn something new everyday, though you would think a better name could have been chosen.