LEANING TOWARD THE FUTURE:THE 3VG (PART II)
(Page 2 of 2)
November/December 1983
Mother Earth News Editors
A CARBURETOR WORTH LOOKING INTO
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Choosing a power plant for a unique vehicle such as the 3VG involves more than simply grabbing whatever unit will fit in the space available. As we mentioned in the main article, the Onan was selected not only for its compact design, but for the fact that its horizontally opposed cylinders limit internal vibration . . . making the engine smoother and quieter than many others of similar displacement and horsepower.
We also considered the Onan's designated application: It was built for use as an industrial powerboat in generato r, pump, and drive systems where continuous opera tion is often the norm rather than the exception . . . and although this would suggest that the engine is all but indestructible, that reliability comes at the cost of fuel economy. (Its L-head configuration, moderate compression ratio, and elementary ignition system and carburetor combine to place dependability above sheer efficiency.)
To circumvent that built-in compromise (and to do so with a minimum of effort), we decided to modify the basic short block externally-by installing [1J a Volkswagen distributor driven off the crankshaft hub and [2] a Qwik Silver carburetor just recently developed (by the Edvac Corporation, Dept. TMEN, 7146 Santa Fe Avenue East, Hesperia, California 92345) for the motorcycle aftermarket. To test the two components individually, we wired the distributor so that we could switch between it and the standard ignition system while evaluating either the original or the high performance carb.
In short, the distributor change proved beneficial, though some fabrication and welding were involved. But the real surprise came with the addition of a manifold adapter and the 34-mm Qwik Silver: Actual highway mileage (at speeds of 40-50 MPH), which with the completely stock engine had been as low as 35 miles per gallon,increased to a high of 53 MPG with the carb fine tuned and the final gearing established at a point suitable for both acceleration and cruising. (In all honesty, this apparent 51% improvement doesn't reflect entirely on the carburetor, since we were also experimenting wick a manifold equalizer bleed circuit.)
Just as surprising was the instant response throughout the Onan's RPM range and the ease with which the carburetor could be adjusted. We studied the design and discussed it with the manufacturer, and it became apparent that the unit incorporated the following features to great advantage: [1] a guillotine slide (which provides a near-perfect, free-flowing venture), [2] a single fuel system (this eliminates fuel wasting transitions between the idle, intermediate, and high-speed stages of conventional carburetors), [3] an internal air bleed (which provides equalized pressure in the float bowl and thus consistent fuel pickup), and [4] a variable tuning needle (the only fuel-metering adjustment in the whole carb). This combination of factors make it not only one of the most efficient and responsive carburetors we've ever come across, but one of the least complicated as well. At any rate, we sure are impressed and it never hurts to pass good news along!
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