Playing With Firewater

PLAYING WITH FIREWATER

“So I says to myself, ‘If I can run on alcohol, why not my bike, too?’

Mike Griffin

Alcohol People gasp. Some of them even shudder when you tell them you’re using alcohol to fuel your motorcycle. There is an aura of exotica about the stuff. To be frank, it’s an ego-tickle to watch mouths gape and forehead veins pop as you tell strangers and cronies alike that your machine uses this fuel. You might even brace yourself for extra dollops of esteem from fellow enthusiasts as they learn you performed this fuel conversion of your motorcycle all by yourself!

Geez, and you thought that “be the first on your block” thrills like this were gone forever when Red Ryder went off the air.

Don’t let all this go to your head.

When people find out how easy the conversion is, your peer group prestige will suffer measurably.

That’s all right, though. By then you’ll be far ahead of the pack.

What Alky Offers the Biker

The fact that engines can realize significant horsepower boosts from the stuff suggests that this exotic fuel, this diabolical brew, is just chock full of energy-charged molecules eager to burst into explosive action.

It doesn’t happen that way; nothing so dramatic.

As a matter of fact, a little research reveals that pound-for-pound alcohol (otherwise called methanol; not ethanol, which is the kind we swill) is pretty tame stuff. For example, one pound of gasoline has the energy potential of about 18,000 BTU. (One BTU, or British Thermal Unit, is that amount of energy required to raise the temperature of one pound of water one degree Fahrenheit.)

In comparison, methanol delivers somewhere between 9500 and 10,000 BTU. So in this respect alcohol comes off as pretty mundane stuff.

What gives?

There is the matter of fuel/air mix.

To achieve maximum power with gasoline in an internal combustion engine, a fuel/air blend of approximately 12:1 is required. On the other hand, alcohol requires a mix of about 5.5:1 for maximum grunt.

Let’s do a little multiplication. Twelve divided by 5.5 will yield 2.18. Next, we multiply 9500 by 2.18, which gives us 20,710. This tells us that alcohol in correct air/fuel proportions provides us with 15 percent more heat energy than does gasoline at its correct fuel/air proportions.

While this works out nicely on paper, in practice the power boost is more on the order of 8 to 10 percent. This is because of the physical variables that creep into the matter; things like alcohol’s chemical affinity for water, which it greedily pulls out of the atmosphere, thus diluting its strength. Also, because of alcohol’s comparatively rich fuel/air blend, the droplets tend to come out of suspension in the intake charge as it passes through port convolutions and such.

Another minus point is cost. Straight, untreated alcohol will cost about $1 per gallon. And if you want to get the best stuff, treated anhydrous alcohol, prepare to spend as much as $1.50 per gallon.

The last bugaboo is that of mileage. You can expect to use at least twice as much alcohol per mile as you would gasoline. This could be a serious problem for desert racers and others given to relatively long rides. Big-bore two-strokes, which typically yield poor mileage when ridden hard, will surely require the installation of larger tanks.

What Do I Hafta Do?

In theory it’s simple. In practice it is equally simple . . . usually. Generally, all you have to do is double the flow values of all the carb’s fuel metering orifices. Often all this requires is the swapping of a few jets. However, if the jet sizes you need aren’t available, you’ll probably have to locate someone with a set of Weber jet drills, then drill your original jets to size.

Owners of common carburetors have things relatively easy, though. If your bike is equipped by Mikuni for example, you’re way head of the game because Mikuni/ Sudco offers comprehensive literature detailing jet dimensions and availability.

Don’t leap in willy-nilly. There’s a hitch.

Some carburetor jets are classified with regard to fluid flow; the number standing for the number of cc of fuel passing through the jet in a given time. Other jets are classified according to jet aperture diameter. In other words, if such a jet is stamped # 130, that means the fuel metering aperture is 0.130mm diameter.

The Mikuni flow-rated main jets in your carburetor are replaced by doubling (more accurately, multiplying its number by 2.15—be safely on the rich side) the number on the jet. Flow-rated Mikuni main jets are identifiable as hex-headed jets. There are large-hex and small-hex jets, but they are both flow-rated, so there’s no reason to get confused here.

Mikuni’s round-headed jets, on the other hand, are classified by aperture size. In order to double the flow of these jets you have to do a little arithmetic. This is because merely doubling this jet family’s size yields flow rates far removed from what you want. What’s required here is a doubling of the aperture’s area. Doubling aperture diameter yields this and then some. For example, let’s assume that we have a #210 round-head main jet. To double flow, we calculate aperture area (a = 7rr2) and come up with 0.00537 sq. in. This is the number we double. Thus 0.01074 sq. in. is the area of the jet we want. This corresponds to a #297.5 main jet. To be safe, though, let’s multiply the area by 2.15, which gives us a desired jet area of 0.0115 sq. in. This corresponds to a #307.5 jet. But there’s a slight problem: The large round-head jets go up to #250 maximum. Because of this you’ll have to drill to 0.3075mm, or 0.121 in. diameter.

Okay, that takes care of the main jet. But there are a few more carburetor circuits to deal with.

Then there are alcohol’s burning characteristics. In terms of combustion by-products and leftover fung in general, alcohol leaves precious little at all. In four-stroke engines minimum if any deposits should be expected. The only things you might see are a white or light beige coating of powder on the spark porcelain, and perhaps similarly shaded residues on the piston crown and exhaust valve. Sometimes you might not encounter any such deposits on the piston at all, leaving it as shiny as the day it was installed.

Much of the above applies to twostrokes, except that while alcohol combustion residues may not be evident, there will be deposits left over from burned oil. These will, of course, be a light grey-brown in color, or maybe even dark brown or black, depending on how much of what type oil is used, the type of riding you do and the amount of time between cylinder head removals.

What About the Minuses?

We mentioned earlier that alcohol has a strong chemical attraction for water. It literally pulls H20 out of the air. If you merely left a container of laboratory-pure, spectral-grade alcohol opened and exposed to the atmosphere, within just an hour or so your 100-percent alky could actually be diluted down to maybe 95 percent pure.

How does this affect your engine?

Well, if you park your motorcycle for a couple of days with alcohol in its tank, the fuel would be drawing water from the atmosphere all the while. Remember, fuel tanks are vented to the atmosphere. In light of this it would be wise to either plug the tank vent when the bike was to be dormant for a while, or to drain the alky into a completely sealable container.

Alcohol’s affinity for water also makes it necessary to turn the fuel taps off and run the engine dry if the bike is to be parked for more than a couple of hours. This is because the H20-laden alcohol could cause rust in the engine and deposits in the float bowl. The latter is characterized by a layer of grey-white goo in the bowl or a dry, white film sticking to the float and walls and floor of the bowl. This layer can be quite thick, impeding free movement of the float and needle valve.

And then there is the problem of carburetor throttle slides. Almost all of today’s carburetors are made of cast aluminum (and the majority of those that aren’t are made of magnesium). Some of these aluminum carburetors come fitted with aluminum throttle slides. Because of > frictional characteristics existing between similar metals, there exists a tendency for aluminum slides to stick in aluminum throttle bores. Straight gasoline has a slight lubricating quality, and for this reason the aluminum carb pieces can get along in relative harmony. However, alcohol has no such lubricating quality. This tendency to stick becomes almost a certainty, at which point you’re likely to experience highly unpleasant surprises. Fortunately, chromeplated brass slides are commonly available for most of these same carburetors. The frictional characteristics existing between the chrome and aluminum surfaces are excellent for use with alcohol fuel.

Alcohol is not compatible with most types of fiberglass. This can prove to be a real hassle if you’re not prepared for it. However, the manufacture of fiberglass fuel tanks today is not as common as it was a few years ago. Instead, most aftermarket non-metal vessels are made of various kinds of plastic. For example, WKR’s tank, made of cross-linked polymers, handles alky with impunity.

Where Does the Real Power Come From?

It’s no secret that the compression ratio of an engine has a direct bearing on how much horsepower is produced. And that the limiting factor with c.r. is the ability of the fuel used to resist detonation: The lower a given fuel’s threshold of detonation, the lower the c.r. must be for safety.

Interesting thing about alcohol. The fluid doesn’t mind high compression at all. Matter of fact, it thrives on it. Premiumquality gasoline, the kind you can’t get at the pumps any more, will perform reasonably well up to about 11:1 c.r., after which point the engine commences its detonative death rattle.

Alcohol, though, is happy right on up to 15:1.

Another factor contributing to the alkyfueled engine’s comparatively greater power output is its latent heat of evaporation. To illustrate: Dip your finger in a little gasoline, then hold it up in the air (discreetly). Notice how your finger soon feels cool as the gasoline evaporates? Now do the same thing with methanol. Yikes! Why with this stuff the finger gets cold. Not only that—it gets cold fast.

And that is a tangible example of the relative differences in latent heat of evaporation between gasoline and methanol.

How does this affect engine performance?

Well, Sir Harry Ricardo, in his esteemed book The High-Speed Internal Combustion Engine, tells us that

“. . . the latent heat of evaporation (of alcohol) plays a supremely important part, and results in a really marked increase in power as compared with other fuels, although the total internal energy of unit mass of mixture is lower than that of either petrol or benzol.

“. . . the power output with atmospheric induction increases very considerably when a very over-rich mixture is used, because more fuel is then evaporated, the temperature of the charge is lowered and the gain in weight of charge considerably more than outweighs the loss.”

What Ricardo is saying, basically, is that the higher the rate of evaporation of a fuel, the cooler things will be through the intake duct, and the denser the intake charge will be. And, of course, the denser a charge is, the less space it occupies, and the more of it can be crammed into the engine.

Voilà! More poop.

Alcohol’s latent heat of evaporation is about 512 BTU/lb. Gasoline, in comparison, comes across as pretty meek stuff in this area, registering about 130 BTU/lb.

The evaporation of alcohol does indeed cool things down in a hurry. As a matter of fact, an alcohol-fueled bike can be ridden hard for a long time on a hot day an¡3 its carburetor and nearby cylinder material will actually be cold to the touch.

Inside the engine things also tend to operate at much cooler temperatures as well. And when you take into consideration the relatively irregular cooling patterns of an air-cooled cylinder, with highwear hot spots here and there, alcohol’s cooling effect comes as welcome relief. Wrist pins, pistons, rings and valves reap particular benefit from this effect, and it tends to increase their lifespans dramatically. Furthermore, it is the poor, beleaguered two-stroke, with its high speeds, marginal lubrication and minimal piston bearing area (big ports mean that much less cylinder material to support the piston) that really appreciates alcohol’s therapeutic influences. The heat stresses imposed on ring-ding powerplants can easily reach destructive levels if careful maintenance, tuning and riding techniques are not observed. The use of alcohol doesn’t obviate these concerns, but it does make them a lot easier to live with.

Logically, let’s start with the starting, or mixture enriching, circuit. In Mikunis and most other modern motorcycle carburetors the principle of operation is the same; when you push the start lever a passage to outside air is opened in the carburetor. Ingestion of this air causes extra gasoline to be fed to the engine as well. Flip the lever back and passage is plugged up. Sometimes flow through these passages is regulated by jets, allowing a modicum of tunability. Often they are just holes drilled in the carb body. Of course, these are not adjustable. However, if your carburetor is not tunable here, don’t despair. In many alky conversions, including the author’s 250cc play bike, no adjustments were done for this reason, and none were necessary. If anything, cold starting is easier than with gasoline.

Mid-range metering is controlled by the needle jet and its metering needle. It is at this point that the Sudco/Mikuni catalog is of valuable help. Super-fastidious tuners will want to re-bop both metering needle and needle jet. However, we’ve seen many alky conversions, our own included, that required only replacement of the needle jet itself; the stock metering needle works just fine. Remember, twice as much metering aperture area in the metering jet. So, if your machine is fitted' with, say, a 159-P5 jet (aperture area 0.0094 sq. in.), it can be replaced by a 159-Q4 jet (area 0.020 sq. in.).

Float level changes? None required in most conversions. However, as long as we're in the neighborhood, let’s take a peek at the float. If it’s made of plastic, you might expect some problems from exposure to alcohol. With luck, and with the wide variety of Mikuni parts available, you’ll be able to slip in a metal float instead.

Pilot jets pose no hassles with Mikuni carbs, because they are all flow-rated sizes. If you have a #35, put in a #70. The only hitch you might encounter is that Mikuni pilot jets are available up to a #80 maximum. We have heard of motorcyclists in a pinch finding that while maybe a #95 jet might be required, the #80 yields excellent results.

Our friends at Mikuni tell us that a throttle slide of less cutaway might be required. For example, if your machine has a 2.5 slide and it burps and spits right off of idle, a richer (less cutaway) 2.0 slide can be installed in minutes.

Don’t expect to fiddle a lot with spark plug heat ranges; that which works well with your gasoline-fueled engine should be very close to ideal. If not, one step warmer might do the trick.

And that’s it. That’s all the average biker will have to do in performing the alky swap. Sure, there will be exceptions. There will be bikes that will mysteriously refuse to respond to the changes we’ve outlined here. But by far and away, the conversion as described here will deliver excellent results for 99 percent of the bikes made today.

No, you probably won’t have to fiddle with oversize fuel taps and lines. But yes, if you live in a cold climate you might encounter cold start and even carburetor icing problems. And these are real considerations that just might make the use of alcohol as fuel too troublesome to bother with.

However, you won't know until you try. If all you need is a carburetor parts catalog and maybe a buck or two for jets, it’s one of the least expensive adventures in the world of high performance.