Lawnside Classic: The Mow You Know

Better carburetors, too, but sometimes not. Look at this Tecumseh gas tank, air filter, and don’t-call-it-a-carburetor setup:

It was factory equipment for a couple of years in the mid-late ’60s on Sears Craftsman mowers—do see the 1966 Popular Science writeup—so the design priorities would’ve been (1) cheap, (2) cheap, and (3) cheap. Even so, the nearly featureless 20″ push mower in the article had a 1966 price of $85, or as we say in 2022, $759 (y’think that’s a gobstopper? The aforementioned fabulous Toro was about $988 worth of mower in 2022 dollars!).

Engines with this –carburetor– had no speed governor per se: no air vane, no flyweight assembly, no linkage. The system, in theory, used airflow through the venturi/intake pipe to limit engine speed to 3800 rpm, which wasn’t a concern in the ’60s but was unnecessarily fast (extra wear and tear; greater consequences of striking something immovable, extra noise…) and is considered dangerously fast today when most rotary mowers run at around 2800 rpm. I say this –carburetor– used airflow-based speed management “in theory” because I’ve never found anyone who remembers these mowers fondly. They seem uniformly panned as hard starters and poor runners. Note the very shallow fuel tank, which was to minimise the tendency of primitive –carburetors– like this to provide a richer or leaner mixture depending on how high they had to lift the fuel out of the tank, which in turn depends on the tank’s state of fill. Tecumseh recognised this was a pile of poo, and didn’t do it again. Briggs & Stratton made extensive use of this kind of simple suction carburetor, which is apparently known as “self-lift” carburetors in the patent world. The Briggs item was marketed as “Vacu-Jet”, and was somewhat less minimal—it was controlled by an air vane speed governor and worked passably well. Don’t forget, set the mixture with the gas tank half full so it won’t be too rich at full or too lean at empty.

Let’s make it a trifecta: Tecumseh brought out capacitive-discharge electronic ignition in 1978, and Briggs launched their “Magnetron” system in 1982, but Clinton figured out how to get rid of breaker points in 1961: a “Spark Pump” mechanically-actuated piezoelectric ignition system devised by Clevite.

PopuScien

Y’know that red plastic pushbutton on a gas barbecue or fireplace? One push, one Clack!, one spark? This is like that, but pressed mechanically once every compression stroke by a lobe on the part of the camshaft that extended above the roof of the crankcase. It was commercialised successfully, but not extensively; Clinton’s market share never approached that of Tecumseh or Briggs (who apparently also invented a piezoelectric ignition system, but never marketed it).

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