Ode to the Carburetor

Once upon a time, there was a simple mechanical device that fed fuel to your car’s engine. It had no electrical hook-ups, was not dependent on sensors nor controlled by a computer. It was held in place by four bolts and could be physically removed from the engine in less than five minutes with basic hand tools. Its workings were visible — and so, comprehensible.

This miracle device is the carburetor.

You can still find them, too — just not under the hood of any car built since the late 1980s. Lawnmower engines, weed whackers and other outdoor power equipment still use them. Probably not for long, though. And here we come to the why carburetors are no longer found under the hoods of new cars:

They are mechanical devices and cannot adjust themselves to deliver precisely the right amount of fuel (and air) to the engine under constantly varying conditions. This is a problem from both an emissions control and a fuel efficiency point-of-view. The carburetor is jetted to meter so much fuel to the engine. The jetting can be rich (more gas) or lean (less gas) but it cannot be both at the same time.

Nor in between.

The jets — small orifices through which the liquid gasoline flows — are a given size (diameter of the orifice) and that’s that. In some of the more sophisticated carburetors — like GM’s famous Rochester Quadrajet — the flow through these jets can be modulated by tapered metering rods that move up and down within the orifice, increasing (and decreasing) the amount of fuel that can flow through the jets. But the range of metering adjustment is mechanically limited; the extremely fine control possible with fuel injection is not possible with a carburetor.

And there is another problem.

In a carburetor, liquid gasoline is pumped (via a mechanical fuel pump, usually) into a small holding tank called a fuel bowl inside the carburetor. Some of this fuel inevitably leaks into the engine, where it dilutes the oil — reducing its ability to lubricate internal parts and also shortening the useful life of the oil (necessitating more frequent oil and filter changes to avoid premature/excessive wear and tear).

Some of the fuel also leaks outside the engine — evaporating into the air.

These are evaporative emissions — and while the smell of gasoline in the morning is a fine thing indeed, it’s a big no-no these days. And it’s not a fixable issue with carburetors, because their design requires they be vented — open to the atmosphere.

Fuel sitting in the bowl is sucked through the carburetor’s jets by the vacuum of the running engine. Air is drawn through the carburetor and mixes with fuel; the resultant air-fuel charge is “inhaled” by the engine through an intake manifold (the thing the carburetor sits on) into the individual cylinders.

In a fuel injected system, the fuel is injected under positive pressure into the engine. Modern systems have injectors positioned directly ahead of each cylinder’s intake valve(s). Air is still “inhaled” by vacuum but it is not mixed with fuel until it reaches the cylinders.

The gas side of an FI system is effectively sealed; no raw (liquid) gas is present and so evaporative emissions are much lower. This was among the main reasons for the demise of the carburetor. Even if jetted perfectly, gas fumes are still going to escape into the air.

The Dude could abide this — but Uncle not so much.

Which is a shame. Because all cars now sound pretty much the same.

Intake-wise, at least.

There is still the hiss of vacuum. But the signature moan of a Quadrajet’s massive secondaries opening up when you floored the accelerator pedal is as much a thing of the past as the steam whistle. Fuel injection (especially port-fuel injection, which is what’s common these days) is all pretty much the same. Each cylinder has its injector, which sprays the fuel. There may be differences in capacity/pressure, but none of these are aesthetically meaningful. Whether you have injectors that flow 45 pounds of fuel per hour or 33 pounds of fuel per hour, you could never tell the difference by sound or feel.

Much less look.

Carburetors came as two and four barrels — and sometimes, you got more than one. Imagine three two barrel carburetors. Or two four barrels. Maybe a set of 45 pound per hour injectors flow more fuel. A dual-quad set-up still looks a lot better.

Sounds better, too.

But — most of all — a carburetor is involving. Making fine adjustments and tweaks; learning how the thing works — and learning how to work on it. An emotional bond is created; the satisfaction of knowing you fixed it. FI is mostly plug and play.

Which is probably why so few people play with cars anymore.

Comments?

www.ericpetersautos.com

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2 Responses to “Ode to the Carburetor”

  1. Jeff T says:

    Ah, Eric… I remember carburetors. Had ’em on most of the 25-ish cars and trucks I’ve owned since 1980. Unlike your well-written ode to the device, though, I don’t miss them. Until 1987, I would have agreed with you completely, but that year, while I was enjoying a big-block ’69 Roadrunner, my dad bought a new Mustang GT.

    Initially, I scoffed, but after looking into the test specs for each car, I found they had basically identical quarter-mile performance, with the Mustang delivering up to 25 or even 30 MPG on the highway, while my Mopar gave me about 10 MPG. Plus, with it’s 3.55 rear gears, the Mopar was spinning at about 3500 at 65 MPH, making it a terrible highway car. That darned Mustang would cruise all day at 100-plus.

    The final nail for me was when the RR’s Holley carb caught fire one day, ruining the paint on the hood. Hated carbs from then on. Now, I drive a turbo four-powered Mercedes, which gets 30+ MPG and does 0-60 in seven seconds, while my last car was a 2011 Mustang GT with 412 fuel-injected horsepower.

    While I would like to have a car with far fewer ‘nannies’ and ‘safety’ devices built in, I wouldn’t go back to a leaking, constantly-out-of-adjustment carburetor on a bet.

  2. RichK says:

    Jeff T is right. I missed the Woodstock festival because I stayed home to center the jets and adjust and sync the dual SU’s on my MGB. (Maybe I was better off?) Like most real drivers I still have a manual trans and no touch screen or other things that impede or dumb down driving. But driving is better, faster, safer, more economical, and almost trouble-free since electronic engine management started. Who wouldn’t rather drive than frequently mess with carbs and distributors? And the best driver in the world can’t separately modulate the brakes on all four wheels.
    Mr. Peters often makes a good point, though, that Uncle has forced the automakers to take good things too far. The great advantages of electronic powertrain management are now being used to take away our freedom, spy on us, and ruin the driving experience while catering to the lowest common denominator. Don’t you wish that “progress” had slowed or stopped about 15 years ago?