Build Dual Fuel Carburetor

The ability to back up your wood-gas power with gasoline can be an inexpensive convenience. Our dual fuel carburetor designs will allow you to do it.



Dual Fuel Carburetor - Ford Autolite carburetor
The modified Ford Autolite/Motorcraft 5200 dual fuel carburetor mounts to our 6-cylinder Chevy sawmill powerplant with a home made adapter box.
Photo by MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - 1, 2, and 3
[1] The parts removed (after separating the air horn from the main body) from the Pinto carburetor include ?clockwise from the top ? the choke thermostat assembly, two casting bosses (cut from the main body's upper left side, next to the primary bore), the secondary booster venturi, the brass vent fitting, the fuel mixture stop pin, the distributor vacuum advance fitting, the secondary main metering jet, main well tube, idle jet, high speed bleed, and operating lever. The center group includes unneeded choke parts. [2] Place the body in a vise and ? using a 1 1/4" hole saw ? bore an opening into the rear wall of the secondary barrel, centered and 1 7/16 inches up from the base. [3] Cut a 3 1/2" length of 1 1/4" thinwall chromed sink drainpipe and slide it into the opening so it butts against the shoulder of the booster venturi slot. Mark the cutting line with a felt-tip pen, using the barrel's wall as a guide, then cut along the mark with aviator's snips.
MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - 4, 5, and 6
[4] These matchsticks indicate the holes that'll need to be filled with epoxy (we used a two-part pliable type that could be blended and formed like modeling clay). The pen tip points to a channel that feeds the power valve, and therefore should not be plugged. [5] The ported vacuum orifice for the distributor advance (at pen point) and the vacuum feed for the choke get sealed as well. [6] The wood-gas inlet pipe should be carefully fitted and fastened to the carb body with epoxy. When that's done, check again to make sure the power valve feed channel isn't plugged.
MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - 7, 8, and 9
[7] Remove the choke shaft and cut it in half, midway between the two center plate-mounting holes. [8] Cut two pieces of 1/8" welding rod to 1 7/8" in length, flatten one end of each, drill a 1/16" hole through both flat parts, bend each rod to a 90? equilateral, then silver-solder or braze the rods to each choke plate where shown. [9] The independent choke shafts and plates are reassembled within the air horn, and the control cables are fastened as indicated (note the tension spring on the wood-gas choke flap lever, and the homemade clamp that holds the cables tightly to the air cleaner housing.
MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - control cable
The air/fuel ratio on our truck's V-8 engine can be regulated, in the wood-gas mode, by a control cable connected to the secondary choke flap.
MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - after 15,000 miles
Here's the dual fuel Quadrajet after doing 15,000 miles on our Chevy's V-8.
MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - modified dashboard with levers to switch between carburetors
A twist-grip throttle and two bicycle shift levers serve as inside-cab wood-gas controls.
MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - 10, 11, and 12
[10] The choke flap cables pass through 3/16" holes drilled in the filter box and element. [11] The modified carburetor and all the parts necessary to mount it to the engine of your choice. [12] Here's the assembled package, ready to go. A standard radiator hose can be used to connect the Garb's smoke inlet pipe to the wood-gas generator's outlet tube. Note that the gasoline throttle lever is offset from that of the wood gas. We've installed stop arms on the latter control to allow idle position adjustment and prevent the throttle blade from opening beyond a 90? angle. (The apparatus should be compatible with any size engine up to 300 cubic inches.)
MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - 13 and 14
[13] To make the modification process simpler, the carburetor should first be cleaned in solvent, then disassembled into its three main parts (air horn, main body, throttle body). The parts that get removed in the course of the operation are, from left to right, the entire secondary linkage unit (and choke rod) ... both secondary main discharge nozzles, main well air bleed tubes, and accelerator tubes (center: top and bottom) ... the secondary metering rods, their two-part lever, and a mounting screw and hinge pin (middle center) . . . the secondary bore baffle . . . and a 1 1/2"-diameter section of the main body's rear wall. [14] With the air horn inverted, remove the brass air bleed and accelerator tubes from both sides of the secondary circuit.
MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - 17 and 18
[17] remove the secondary linkage assembly from the throttle body. [18] Using a 1 1/2" hole saw with a 1/4" pilot bit, carefully drill into the rear wall of the carburetor's main body until the saw penetrates the divider between the two rear barrels to a depth of one inch. (The pilot bit should be set to bore no farther than the mounting slot for the secondary baffle, and the cut should be centered both horizontally and vertically.)
MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - 15 and 16
[15] The larger main discharge nozzles should be pulled out as well. Once these brass parts have been taken out, you can seal the six holes with pliable epoxy. [16] Slip the secondary bore baffle out of its slots.
MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - 19 and 20
[19]Remove the hole saw, then using a No. 12 bit, intersect the main cut, making sure to drill only deep enough to ... [20] separate the newly formed plug from the rest of the body so it can be pulled free. With that done, dress the opening with a file to smooth any rough edges.
MOTHER EARTH NEWS Staff
Dual Fuel Carburetor - create a cutting guide
[21] Cut a section of 1 1/2" thinwall sink drain to about 3 1/2" in length (you can use either a straight or an elbow fitting, depending on where your wood-gas feed hose enters the engine compartment), then slip it into the opening and mark a cutting line on both its sides, using the carburetor's walls as a guide.
MOTHER EARTH NEWS Staff
Dual Fuel Carbuetor - 22, 23, 24, 25
[22] Clip the drainpipe to form a contoured "fishmouth." [23] Place the pipe in position, then drill a 1/8" hole through the carb body's upper gasket surface (between the two oblong holes as shown) and the wall of the pipe beneath. Countersink the bore 3/32 inch with a 5/16" bit in preparation for installing a 1/8" x 3/8" countersunk pop rivet. [24] Fasten the pipe to the carb body and check to make sure the rivet's head is flush with (or below) the gasket surface, then knockout the small nailhead left in the rivet with a 1/16"" pin punch. [25] Seal the joint between the pipe and the carburetor body with silicone compound
MOTHER EARTH NEWS Staff
Dual Fuel Carbuetor - 26, 27, 28
[26] Cut apiece of 1/8" x 3/4" flat stock to 3" or so in length, drill a 3/16" hole in each end and another that's offset a bit from the center, and tack-weld this lever to the end of the secondary throttle shaft to replace the small arm you removed previously. If you want to use a motorcycle twist grip control as we did, crimp a ring tongue terminal to the end of the cable and mount it to the lever. If not, standard linkage hardware can be used. [27] Drill a 5/32" hole through the lower arm of the secondary choke shaft lever and fasten a cable-and-ring control (as shown) or a ball-and-socket terminal. A bracket ? made from a piece of 1/8"" X 5/8"" X 4"" flat stock bent to a 90? angle ? can hold the cable in place. [28] The modified carburetor, assembled and ready for installation. A 1-1/2"" radiator hose completes the joint between the smoke supply tube (from the wood-gas generator's cooler/filter) and the sink drain inlet pipe fitted to the rear wall of the altered Quadrajet.
MOTHER EARTH NEWS Staff











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