Mother's Dual-Fuel Alcohol-Powered Van!

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So—armed with flat and needle-nosed pliers, a screwdriver, a wire gauge set, and a complete assortment of drill bits (numbered sizes 1 to 80, plus one 19/64" version)—MOTHER's car doctors prepared to perform surgery on the alcohol-carburetor-to-be, after first dismantling the unit and cleaning it thoroughly with solvent. (This preparatory operation included the removal of the press-fit plugs that sealed the factory-drilled fuel passageways from the outside.)

The first step involved enlarging the main jet from .080" to .104", for a total diameter increase of 30%. Then the accelerator pump discharge nozzle diameter was increased by 20%, from .025" to .030". Next—to improve the engine's transition from idle to cruising speeds—the idle transfer slot (part of a circuit that supplies nearly all of the necessary air/fuel mixture during normal driving at speeds below 40 MPH) was expanded from .020" to .059", and two .043" holes were drilled at the "upstream" end of the slot, in line, to further enhance smooth performance during "off idle" operation. Finally, the idle screw passageway leading from the needle's tapered tip to the throttle bore was enlarged—to provide a wider range of adjustment—from .066" to .076", and the float height was raised by 3/16".

At that stage of the conversion, preliminary testing indicated that, although the carburetor was fairly well calibrated according to the exhaust analysis equipment, there was still a slight hesitation in the transition from slow to midrange speeds . . . and the higher float level resulted in an occasional fuel "dribble" into the carb throat through the main booster jet outlet.

The second phase of modification, then, included drilling a "sight hole" in the side of the float bowl so that the port's lower edge was about 1/10" below the dripping orifice, plus visually setting the float to eliminate the leakage and tapping the inspection hole so a threaded brass plug could be installed after final adjustments were made. In addition, all the idle circuit passageways within the carburetor were drilled out to .149", and the idle fuel restrictors and other potential problem areas (such as gasket perforations and casting burrs) were altered or removed.

At the same time, the idle fuel jet in the main well was increased in diameter from .024" to .039", and the idle air bleed was enlarged by 62%, to .073". (These alterations were made to increase both the amount and velocity of air/fuel mixture delivered to the engine from idle to 20% of full throttle position.)

Final alterations were as follows: Both the primary and secondary main fuel wells were enlarged to .300" in diameter (these reservoirs hold a supply of fuel "in waiting" between the main jet and the venturi supply tubes, for use the instant the throttle is cracked open . . . thus providing the extra-rich fuel mixture to the engine as soon as it's needed), and a main well air bleed was added, by drilling a .025" hole—obliquely—from a point near the top of the secondary main fuel well directly into the carburetor throat and ahead of the booster venturi section of the carburetor. (This passageway—a standard feature on newer carbs—supplies positive air pressure to the fuel wells to insure faster liquid movement and better response.)

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