Just inherited a 1969 Porsche 912 from my father. I have a general understanding of fuel injection from my days drag racing my nitrous assisted ’86 300ZX but I have no clue how a carburated car works and online articles are beyond me. Need the 5yo explanation because right now, it’s basically dark magic.
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When the engine turns, each cylinder will suck air in its intake stroke. This sucks air from a manifold. Upstream of the manifold there’s the carburetor. Now we said that the engine is sucking air right? Ok that air is sucked through the carburetor. The carburetor is a Venturi pipe, goes wide-narrow-wide. In the narrow part the air is the fastest and has the least pressure. In that narrow part of the carburetor there is a fuel jet. The depression of the air will suck fuel from that jet. The carburetor has also a valve that regulate the air, it’s the throttle. The more you press the accelerator the more air is let in toward the engine. Basically the acceletator control is working by deciding to choke the engine more or less, full throttle the valve is fully open and the engine can get all the air it can suck, when accelerator is fully released the valve will choke the engine to a point it can just idle at minimum rev.
The magic is that the more air you let in the more suction there is on the fuel jet, this will automatically give the right mixture air/fuel without the need of any electric or electronic control. The carburetor includes a little fuel tank that feeds the fuel jet. The tank is kept always at the perfect level by a float and valve assembly. A fuel pump takes the fuel from your tank to this valve that feeds the carburetor tank.
So the carburetor is a very well made shaped pipe with a fuel jet and an air valve and if tuned properly, it does all you need by using just a mechanical link to the accelerator pedal.
Being completely passive and mechanical, tuning, cleaning and maintenance is essential to keep it working properly. It’s not a computer, can’t self adjust. If it gets out of tune it will perform really bad.
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