Fuel Conversion: An Experimental Dual Fuel Truck

With the right tools and know-how, you can carry out an alcohol fuel conversion in a few hours.
By the MOTHER EARTH NEWS editors
September/October 1979
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The first conversion step is to remove the air horn from the float bowl.
MOTHER EARTH NEWS STAFF
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There's certainly nothing special about a 10-year-old pickup truck, but when that same vehicle can drive—indefinitely—without ever having to stop at a gasoline station to fill up ... well, then the highway veteran becomes something worth writing home about!

No, MOTHER EARTH NEWS hasn't developed a perpetual motion engine, but her researchers have succeeded in adjusting the above-mentioned vehicle's powerplant so that it runs on pure homemade alcohol fuel. The fuel conversion wasn't at all difficult, either. In fact, it can be done (in less than two hours!) on just about any vehicle manufactured today with tools you'd find in most anyone's workshop.

Alcohol Basics

There's no reason for alcohol not to be used as motor fuel. Some of the earliest "horseless carriages" ran on it exclusively, and even in modern times, aircraft and racing cars have taken advantage of the fuel's several benefits:

[1] Alcohol burns clean.

[2] The distilled fuel also acts as a cleaning agent within the engine.

[3] An alcohol-burning engine tends to operate at slightly cooler temperatures than does its gasoline-powered counterpart.

Even aside from these mechanical benefits, there are other less obvious advantages to ethanol fuel ... one of the most important being that it's not dangerously volatile, as is gasoline. Other positive points include the fact that a 200-proof "juice" isn't necessary (Our pickup runs fine using 180- to 190-proof ethanol, and can be operated on fuel with a proof of as low as 160) and that a vehicle's owner can manufacture his or her own alcohol at home after obtaining the appropriate government permits.

Gettin' Down to Nuts and Bolts

Begin your conversion by gathering up all the tools and hardware you'll need to complete the job. In most cases a screwdriver, a pair of needlenose pliers, a putty knife, a set of assorted end wrenches, a vise-grip tool, and a power drill—with bits ranging in size from .0638" (No. 82) to .0890" (No. 43)—are all you'll need. To make your task easier, though, you might want to refer to a Motor, Chilton, or Glenn auto repair manual for exploded illustrations to guide you through the necessary carburetor disassembly. (Another alternative would be to purchase a carb rebuilding kit for your particular make and model. It will not only provide a working diagram, but will also supply you with gaskets and other parts that may get damaged during the stripdown process.) Finally, on most all carburetors manufactured, there is a removable main metering jet. You'll probably want to purchase several of these from your automobile dealer (at a cost of less than $1.00 apiece) so you'll be able to easily convert your car back to gasoline fuel if the need arises.

With these preliminary steps taken care of, remove the carburetor air filter housing—and all its hoses, tubes, and paraphernalia—from the engine. Next, disconnect the throttle linkage from the carburetor, and—if your vehicle is so equipped—any choke linkage rods that aren't self-contained on the carb body. (Older vehicles might use a manual choke. If this is true of your car or truck, remove the control cable and tie it out of the way.) Now unscrew the fuel line from the carburetor inlet fitting and remove any other hoses that fasten to the "pot," including vacuum and other air control lines. (If you're not quite sure that you can remember exactly where all these hoses belong after you've taken them off, it'd be smart to label them and their fittings first.

When the carburetor is completely free from all external attachments, remove it from the manifold. (Single-barrel units usually have only two fastening nuts or bolts, while two- or four-barrel models use four-point mounts. Once the carburetor is off the engine, drain the gasoline from it by turning it upside down, and—if it's covered with grime—take the time to clean the assembly off with an automotive degreasing solvent (but not a carburetor cleaner, which would deteriorate rubber parts).

A "Boring" Explanation

In order to use alcohol fuel in an engine designed to burn gasoline, it's necessary to enlarge the opening in the carburetor's main jet (or jets, if your carb is a multithroat model). Start by removing the air horn from the float bowl. In most cases there will be a choke stepdown linkage rod—and possibly some other mechanical connection—between the two components. Disconnect these, if you can, before unthreading the air horn's fastening screws.

Next, locate the main jet. Some carburetors have the jet installed in a main well support (a tower-like mount fastened to the air horn), while others mount the metering device directly in the float bowl body. In any case, you shouldn't have any trouble identifying the removable main jet: It's a round brass fitting—with a hole in its center and a slot in its top—that threads into place.

Now remove the float assembly, unscrew the jet, and measure the diameter of its central orifice. The simplest way to do this is to find a drill bit that fits snugly into the hole, then determine the size of the bit by matching its drill number to its diameter—in thousandths of an inch—using a conversion chart available at your local hardware store or in a machinist's handbook. (You can also use a micrometer to figure the drill size.)

Once you've determined the "normal" size of your gasoline jet's orifice, prepare to increase that dimension by about 40%. Remember that this isn't a fixed percentage for every engine. You might have to drill several different jets in progressive increments above and below that figure and try them out (by actually running the vehicle) to see how they work.

For example, MOTHER EARTH NEWS' six-cylinder truck uses a .056" main jet to operate on gasoline. By enlarging the hole 40% (to .0784") with a No. 47 drill, we made the opening just about right (in fact, that increase was almost perfect on our particular vehicle) for alcohol fuel. If the orifice is too small, it won't allow enough liquid to enter the system and the engine will backfire and miss. (It may also burn valves if left in such a lean condition for an extended period of time.) On the other hand, if the jet is over-enlarged, the mixture will be too rich and you'll waste fuel.

Be sure to hold the jet with vise-grips while you carefully bore out its central hole and, if possible, use part of the carburetor itself as a "mount" when you drill. (If you do this, be sure to clean any brass residue out of the carburetor and its components.)

Some carbs—such as the unit on our truck—will need additional idle-circuit enlargement if they're to run properly. To accomplish this easy chore, remove the idle-mixture screw and drill into its orifice with a bit that's slightly larger than the original hole. Be cautioned, however, that this alteration doesn't apply to all types of carburetors. It would be best to install the carburetor—with only the main jet enlarged—on the engine and try it out before drilling the fixed idle circuit.

The final change that our mechanics made in the carburetor was to shim the idle-mixture screw spring with a couple of small lock washers. This allowed the threaded metering device to be drawn out farther than normal without danger of its vibrating loose. (They also tightened the idle-speed screw by about 1 1/2 turns.)

With all the modifications completed, replace the main jet in the carb, install the float, and reassemble the carburetor. Position a fresh gasket on the manifold (make sure both metal surfaces are clean) and bolt the carb assembly in place.

Dual-Fuel Plumbing

At this time, if you choose, you might want to rig up a dual-fuel system. This will allow the use of either alcohol or gasoline (with a bit of tinkering involved in the switch-over process) and entails only the installation of a second fuel tank and some additional plumbing.

Start by looking your vehicle over and deciding where you want to put your extra tank. On our pickup, the container fits perfectly between the cab and the rear fender, but on a passenger car it might have to be mounted next to the regular gasoline tank (and away from the hot-when-running exhaust system, of course). The vessel itself can be anything from a recycled Freon tank to a fuel tank from a small car. Whatever you choose, be certain that the container is leak-free and mounted safely.

Once your car is equipped with a dual fuel capability (our hook-up is illustrated in this Dual Fuel System Diagram), you can begin to attune the vehicle to its new "feed." Reattach the throttle and choke linkages (and any other hoses you might have removed in the conversion process), then drain your petrol tank and fill it with alcohol (you can also—at this time—fill the auxiliary container with gasoline). Shut off the valve that supplies the new secondary fuel pump, open the alcohol control, and start'er up!

It'll take a few seconds to fill the empty float bowl, but the engine should soon start and run at a fast idle. Slowly decrease the RPM's of the engine by backing off on the idle-speed screw until the engine wants to stall. At the same time, it may be necessary to gradually adjust the idle-mixture screw—by 1/4-turn increment—until the engine's "roughness" evens out. Eventually, the vehicle should idle nicely (though it may run slightly faster than usual).

Now replace the air cleaner housing and take your car for a drive. It should perform normally. After driving about 10 miles at cruising speeds, it's important that you remove the spark plugs and check their electrodes. If the tips are covered with a white coating, the combustion chamber is getting too hot. Dismantle the carburetor again and enlarge the jet by one drill size (remember: the lower the number, the larger the bit). Test the car again and recheck the plugs. They should be covered with an even, light tan coating.

Fine Tuning Tip

Remember that every engine is different. As such, each will require a bit of "fiddling" before it will operate normally. If your alcohol-powered convert doesn't perform to your satisfaction, there are several remedies you can try.

First, advance the timing several degrees by turning the distributor housing opposite to the direction in which the rotor spins. (Don't overdo it, or the engine will "ping" with pre-ignition.) You can also disconnect the vacuum advance line to the distributor and plug it with a screw or ball bearing. This will prevent a too rapid spark advance. You might try closing the gap in the spark plugs by .004" to .006", too. If you care to get more involved, raising the compression ratio—either by simply "milling" the head or by installing high-compression pistons—will improve both engine performance and fuel economy.

It may, of course, prove impractical—because of the unit's particular design features—to alter your car's original carburetor. The best solution in such a case would be to buy a rebuilt carburetor of an older vintage. The bolt patterns on most manifolds haven't changed for a decade or more, and nearly all carburetors made in the 1960's can be converted without trouble.

The Bottom Line

Mother's pickup is still going strong after over 5,000 miles. It starts easily in the morning and runs well when it reaches operating temperature (we've found that a manual choke aids in the "warming up" process). Fuel economy isn't quite as good in the alcohol mode, but it's close to normal. Power and acceleration are unaffected.

Again it's important to remember that our truck is experimental, not perfect. Keep an eye on your converted engine and be ready to spot a problem before it gets serious. We have big plans for the future, though, and—as each new issue appears—we hope to have a few more improvements for you, beginning with a wintertime starting system.

EDITOR'S NOTE: Though the federal government—as well as many states—has acted to eliminate road use taxes on renewable fuels, it may be illegal to operate your alcohol-powered vehicle on highways in certain states. Check with your state authorities before you venture out on public roads. 

And, if you'd like to be able to distill your own ethanol fuel, MOTHER EARTH NEWS' Alcohol Fuel Kit—with still plans, mash recipes, and details on applying for a Bureau of Alcohol, Tobacco, and Firearms permit—is just what you need.   


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