I remember a thread that discussed this, but when I tried to use the search function, it could find no matches. The Primer/mixture lever has me a bit confused. I know that turning it one way leans the mixture, the other enriches it. My problem is which way is lean, and which is rich? When you pull the lever out does it allow gasoline to flow, or does it restrict the airflow?
The mixture screw going through the firewall to the carb adjusts fuel. Counter clockwise gives more fuel and clockwise less fuel to the engine.
A 26/27 setup, pulling the knob out closed the choke for priming (if it's hooked up), turning that same knob clockwise (in) leans the mixture counter clockwise (out) makes it more rich.
Twisting the mixture control counterclockwise adds more gasoline to the air/fuel charge
entering the intake manifold. -That's a richer mixture. -Generally speaking, a richer mixture
will cause the engine to run cooler.
Twisting the mixture control clockwise subtracts gasoline from the air/fuel charge entering
the intake manifold. -That's a leaner mixture. -Generally speaking, a leaner mixture will
cause the engine to run hotter.
Theoretically, the engine runs cleanest and most efficiently when the air/fuel mixture is
"stoichiometric." -That's a needlessly fancy word which means all the gasoline and all the
air that goes into the cylinders are completely consumed, leaving neither unburned gasoline
nor air in the exhaust gases. -What's left—again, theoretically—would be carbon dioxide,
water vapor, carbon monoxide, and various nitrogen or sulfur oxides.
In practice, adjust your mixture by running your car at a fast idle with the timing advanced
for normal driving and twist the mixture knob either way until the idle RPM peaks. -Now
you're in the ballpark. -From that point, adjust no more than about a quarter-turn either
way for best acceleration.
After a weekend of driving, pull your plugs, inspect and read them according to this chart:
Here is a list of when and why you may want to adjust the mixture:
The choke restricts the air intake but allows the full vacuum of the engine to suck in gas. Do this only for priming a cold engine. On some cars, it might be necessary to choke slightly a warm engine which has been turned off. First try to start without the choke, then if it doesn't start, give it a slight choke. Experimentation will teach you what is best for your particular car.