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I spent a lot of time around carbs.
My 1937 Ford had a passageway right below the carb in the intake manifold, that allowed hot exhaust gas to heat the intake manifold and help with fuel atomization.
The Nissan Z cars from 1970 to 1972 used the SU type carbs. I really like their simplicity and the cars got good mileage. The air cleaner had a flap that you used to allow heated (from the exhaust manifold) into the air cleaner to help with atomization, because the variable venturi carbs were very prone to icing. They also had coolant passageways in the manifold, and it they were not connected the car ran like crap.
Icing is when the air velocity across the venturi area lowers the effective temperature to the point where the fuel will no properly atomise. The plugs will be black. Flip the lever and allow heated air in and the plugs turn light brown (unleaded fuel) to white (leaded fuel).
You will get your best economy with warm to hot air going in the carburetor. The higher density of colder air will pull more fuel than the same VOLUME of less dense air at higher temperatures.
Volume and density are two different factors. Carbs are rated in cubic feet per minute irrelevant of density, but since density affects the vacuum applied to the jets the fuel entering the intake will change based on density. It will also change according to volume.
I like the idea of using oxygen sensors to measure actual fuel mixture, for precise tuning of the carb.
I used a digital thermometer to adjust the manual cable operated brakes in the 37 Ford, by measuring the temperatures of each brake drum after driving and tightening the cables to equal the drum temps.
In the SU carbs we could adjust the float levels without any dis assembly. You could increase the float level by taking the small bolt off the top of the float chamber and using a special tool lift the float up and bend the tab that contacted the needle valve. This raised the float level and allowed more fuel in the chamber.
Mixture adjustments were accomplished by using different needles in the carburetor.
With only the single needle and seat arrangement and no throttle pump the throttle response was amazing. The first time I drove a Z car I could not keep it from bucking when I released the clutch, until I used the heel of my foot to stabilize my clutch release method. The throttle response made my clutch engagement oscillate until I change my engagement method.
regards
Mech
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