Okay this might seem like a dumb question but what is the gasoline regulating needle valve used for (apart from regulating the gasoline)
Is this used mostly for altitude travel? as in making the carb run richer or lean when going up and down mountains... or is it used for adjusting idle? or something totally different...
Back when Model T's were new gasoline quality varied greatly from one supplier to the next. The needle valve allowed the car to function on a variety of gasoline qualities.
Today most gasoline is the same regardless of where you buy it. The mixture valve gets set to where the car runs best when warm. Then you leave it alone.
The Model T carburetor is very simple, newer carbs has more sub systems that takes care of different conditions making it unnecessary to adjust the main jet.
There is an idle circuit though, so it hasn't much to do with idle.
The air up in the mountains has less oxygen, so you may have to adjust for different height above sea level. Another reason to adjust would be to open it slightly for better running while the engine is cold - especially in winter time. Today we don't have to drive in freezing cold weather, so it's not needed on all T's. They're all a bit different - and there were lots of carburetor designs used during the 19 years of production. But they may all need some adjustment from time to time..
A good method is to drive the car in high on a level, straight (and wide) road. Screw in the adjustment until it starts to stumble, screw it out until it also stumbles from running too rich, then screw it back to the middle in between. Often the final adjustment is 1-1.5 turns out from closed. Never screw it down tight - the seat will leave a groove on the needle, making it much worse for fine adjustments. If it's grooved, fix it like Steve shows in this video:
Read answers 42 through 45 in the "Gasoline System" section of the Ford Manual (owners manual):
Automobile owners manuals and the Holy Bible are the most widely possessed yet never read books.
Thanks guys! That video on using 2x4 block file, and electric drill to remove the grove is really great!
Here's a few accessory automatic gas control units for the Model T carburetor.
Here's another three units that use a bi-metallic strip to adjust the mixture.
Check out this past thread on Model T all things Carburetor.
The idea for the video came from the MTFCA carburetor book. Anybody working on a Model T who doesn't know everything about it should have the MTFCA books.