Fueling Around: Better Carburetor Tuning

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We’re bound and determined to get our carburetion ills dialed out. Step one is drilling a hole in the exhaust pipe or collector. Those who don’t recall, our tall-geared, tightconvertered, hot-cammed engine kinda laid down about 100 feet out of the starting line, and didn’t really come back to life until a few hundred feet down the dragstrip. Not a full-fledged bog, just extreme “laziness.” Tired of shots in the dark, we decided to avail ourselves of the latest tuning aid: the UEGO oxygen sensor.

The concept is simple: a spark-plug-sized sensor mounts in the exhaust stream, and generates an output voltage in proportion to the air/fuel ratio. For years, we’ve been using oxygen sensors as a tuning aid, hooked up to one of many aftermarket display gizmos that convert the sensor’s voltage to a comprehensible reading. However, the standard O2 sensor has a fatal flaw, at least when is comes to performance use: While being extremely accurate and repeatable at ratios of around 14.7-14.85:1, and equally accurate at leaner mixes, they are notoriously inaccurate on anything richer, making them ineffective as a performance tuning aid. Consider them an emission and fuel economy device.

The new generation of widerange (UEGO) sensors overcome that limit, but have, until recently, been expensive. Recently, the price of the sensor has dropped dramatically. Most of the devices on the market are space-age-looking rectangular, digital-only displays, something clearly out of place in a ’69 Road Runner. Then we spotted Advance Engine Management’s P/N 30-4211 unit, which combines the latest technology into a ‘60s-style round gauge case, at reasonable price. The AEM has a further advantage of having both a 3-digit LED digital display, and a round LED bar graph of LEDs that are, in effect, an analog, read-it-at-a-glance pointer. The one we picked even has white-on-black lettering.

air-fuel mixture

Old school meets new, and everybody’s happy. Installation was easy, with the only step requiring more than a minute’s work was drilling and welding the sensor’s mounting bung into the header’s collector. We must add, however, that the AEM-supplied instruction booklet was one of the best written, clearest, and most informative we’ve seen. Whoever their tech writer is, he’s got us looking over our shoulder.

Only two caveats here: The exhaust system should be leak free upstream, and at least 10˝ downstream, of the sensor, and the business end of the sensor should always be at least slightly lower than the wiring end to prevent condensation collection at the tip. Now the sensor simply screws in. While the guts are super high-tech, the installation is monkey-wrench simple. For now, we simply lashed the AEM’s display to the side of our existing gauge panel with a cable tie. We’ll probably wind up making a second gauge panel to take the place of the ash tray. The display, being only simulated analog, has right-now response and zero lag and overshoot. It’s super visible, day or night.

The AEM deal comes pre-wired, just plug it in. You only need to hook up one ground wire and a source of switched twelve volts. (The AEM does provide data and raw sensor voltage outputs for use with PCs and dataloggers.) We used a die grinder—you could also use a rat-tail file—to size the hole for the sensor bung.

SOURCE: Advanced Engine Management, 2205 126th Street, Unit A, Hawthorne CA 90250; (310) 484-2322

More by Rick Ehrenberg

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