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In Defense of Manual Chokes

July 24, 2012 by Matt

Choke Knob

Thought about this whilst mowing my lawn Sunday afternoon. The mower had run out of gas in the middle of the back yard, and after a refill, it took me a good minute and a half of yanking on the cord to restart it. The reason for the difficulty? The automatic choke on the mower’s carburetor had reset itself and was delivering a rich mixture to an already-warm engine. Well, that and the float bowl was drained from having run out of gas… But I digress.

It used to be the case that almost all carbureted cars were fitted with a knob or lever somewhere in the cockpit that gave the driver control over the carb(s)’ choke. What does a choke do? In simple terms, it controls the ratio of air to fuel entering the engine. A cold engine needs a rich mixture, and a warm engine needs a lean mixture. Upon a cold startup, the driver would engage the choke, richening the mixture, and gradually back it off as the engine warmed.

But modern engine management has superseded all that. A fuel injection system’s electronic brain controls the A/F ratio far more precisely than a human ever could, and in response to the direct needs of the engine, not a driver’s vague sensing of those needs. Also, unlike another “holdover” from days when drivers had more control over their vehicles—the manual transmission—with which there are substantial, objective benefits over an automatic, there’s absolutely no downside to computer control over the mixture. From an engineering and practical standpoint, EFI is a lock.

So what’s the point? Well, truth be told, this post really is the equivalent of an audiophile pining for the added character of a vinyl record over the cool sterility of the thoroughly superior compact disc. As with carbs in general, the patina of a manual choke control’s presence engages the driver with the car in an irreplaceable way. Yes, it helps to know a bit more about the inner workings of the engine, and no, I wouldn’t pine for the good old old OLD days when drivers had to manage non-synchromesh gearboxes or control spark advance, but so help me, I do miss that little plunger knob on my old RX-7’s dash that read “CHOKE.” Heck, it even had a vacuum servo to retract it in case I forgot to when the engine warmed up, but just knowing it was there…

With respect to how much we let our cars “do for us,” I’m convinced everyone has their sweet spot. Again, there are certain functions I’m more than happy to let automated systems handle. But for my part—and maybe it’s a comfort/security thing—a few more buttons and controls, such as the aforementioned choke knob, would be welcome.

Filed under: Miscellaneous, Technical, Tinkering


  1. John D says:

    …and tachometers, and voltometers, and coolant temp gauges, and exhaust temp gauges (pyrometers?), etc. You can never have too much (optional) involvement with a car or information about the inner workings of said car. I firmly believe the best cars of the future will allow the driver to decide how involved they want to be with the driving/functioning of the vehicle and, conversely, allow them to opt out of almost all involvement if desired. Now how they do this is the tricky part. Center console drive select shifters doing double duty as clutchless and incredibly slow gear selectors is a good example of a decent idea poorly executed. My hope is that the future will bring us the best of both worlds in a way that those of us who still long for manual transmissions (and manual choke knobs). Although, if it becomes an unnecessary control will it still have the same feeling to us? Somehow I doubt it…

    • Matt says:

      “Although, if it becomes an unnecessary control will it still have the same feeling to us?”

      Yeah, there’s the rub. I agree with you that the future is probably an optional level of involvement. But like you said, will it feel the same if we know there’s an electronic intermediary between us and whatever it is we’re “allowed” to control? Hmm.

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