 Techline-Oct09-Evolution Fuel Delivery-Pt I Gassing Up
EVOLUTION FUEL DELIVERY
Part I: Gassing Up
This article continues in the next thread.
This month we start a new excerpt, this one is from Donny’s Unauthorized Technical Guide to Harley-Davidson 1936-Present, Volume III: The Evolution 1984-2000. Some content has been altered to fit AIM’s style and format.
I know this is going to sound stupid, but Harley-Davidsons have different personalities. If your bike does not run well on one gasoline then switch to another brand of gas. It’s amazing how this works on some bikes. I call it Inanimate H-D Schizophrenia. But before you pump your next tank of gas, take a look at what additive is blended into the gasoline and figure out which is best for your Big Twin.
It’s advisable to run at least an 87 octane, quality unleaded gasoline in all stock Evolution motorcycles. Alcohol additives like methanol and ethanol can harm rubber carburetor/EFI components depending on the percentage blended. Modern Harley-Davidsons are designed to run on unleaded gasoline. Unleaded gas is less harmful to the environment. Leaded fuel uses lead as an excellent, but dirty and environmentally unfriendly, octane, which is why it is no longer available at the pump in the US.
Always use gas from national brands, because it is more likely to adhere to industry standards, and purchase gas from a busy gas station because it will get fresh deliveries more often. More frequent deliveries means water and sediment will not get a chance to build up and the fuel does not have a chance to separate into its component parts. The alcohols can separate from the gasoline over time.
Ethanol & Methanol
It’s a good idea not to use methanol-mixed gasoline at all, no matter how low the content. Methanol may cause hard starting and rough running. It will damage fuel system components, especially rubber seals. If you’re in the middle of nowhere and this is all that’s available, use it until you get to another gas station with the proper fuel for your Harley. Half a tank will not hurt in an emergency, but fill up and mix in proper fuel as soon as possible.
The engine management system’s ECM (electronic control module) also known as an ECU (electronic control unit) or ICU (ignition control unit) is programmed to use a specific fuel mix. Ethanol burns at a different optimal air/fuel ratio than gasoline, so a poor running engine can easily be due to the wrong mix. Gas mileage will also be reduced with a higher percentage of ethanol because it produces less heat, which is measured in BTUs (British thermal units). Ethanol fuel may be less expensive, but it makes less heat energy, thus you’ll need to buy more ethanol to produce energy equal to the burning of a smaller amount of gasoline. As with methanol, it will not hurt your engine to temporarily burn a tank of high-percentage ethanol relative to gasoline if that is all that is available. However, use it quickly and refill with the proper gasoline as soon as possible. Ethanol content of up to 10 percent ethanol and 90 percent gas is okay. Avoid higher percentages of ethanol unless in an emergency situation. This is getting tricky, as many gas stations now have ethanol-mixed gas in a 15/85 ratio. Gas pump signage usually has percentage levels of ethanol near the price per gallon notice.
A high percentage of ethanol has other problematic issues that will affect your Harley-Davidson over time. The first is that it is corrosive to sheet metal. Continued use of ethanol requires the use of stainless steel gas tanks. Secondly, it will also peel off tank sealer inside the tank, which is a nightmare to repair, as the sediment constantly bungs up fuel filters and smaller orifices. Thirdly, ethanol attacks rubber gas lines and destroys their usefulness. The rubber used for sealing manifolds and the O-rings in the carburetors and EFI induction systems will expand and just go wonky, leaving fuel to leak and excess air to enter and lean out the engine. Finally, high concentrations of ethanol are caustic, attacking the aluminum in EFI induction throats and carburetor bodies. Viton rubber-based manufactured seals, O-rings, and fuel line will withstand ethanol much longer. Read your H-D manual to determine the allowable percentage of ethanol in gasoline for your year and model Harley-Davidson. However, all Evo models should use 87 octane fuel or higher.
Food shortages, particularly in the third world and emerging economies, are resulting from the more lucrative income offered to farmers growing grains for ethanol production. Defenders say that rising energy prices and fertilizer costs are more of a factor in rising food costs, with ethanol only contributing 15 percent to the rise. Others feel that lobbyists in the oil industry are spreading false rumors and misinformation about ethanol to defeat its usage in gasoline. These ethanol supporters say that the protein and other nutrients are mere by-products; only the starch in the plant fiber is useful for ethanol production. Still other defenders of ethanol point out that this less expensive product keeps the more expensive, oil-based gasoline in check that gas would cost much more without the inclusion of ethanol. The advantages of the alcohols, like ethanol, are that they burn cleanly and offer environmentally safe octane enhancement.
Octane prevents gas explosions and encourages burning at a defined rate. One of the great advances of engine technology in the early 1900s was the discovery of octane, which controls the rate of burn. There are many different octane substances and elements, the best early example being lead. Before octane, haphazard explosions caused the first engines to hack along with much inefficiency. Octane has the ability to stop chaotic explosions and bring order to the combustion chamber. Gasoline is a complex mixture of many chemicals, and chemical components are added and subtracted to enhance the octane rating.
Tetraethyl lead was the old and easy way to get the octane level needed to control detonation. Lead is an excellent octane, but is also corrosive to the internal engine parts, including the spark plugs and exhaust system. Some octanes are oxygenates (MTBE and all the alcohols) that also lean the mixture and diminish power unless gas refiners compensate for the loss.
Enhanced octane reduces harm from detonations inside the engine, but many times produces harm to the environment and to us. Lead, for example, causes mental retardation and learning disabilities in children, and, to a lesser extent, adults. Fear arises because children will put substances in their mouths at one time or another that adults will not, and lead tastes good. Back in the day, engine exhaust left lead residue everywhere on the ground and in the soil where children play. Successive octanes did not wreak havoc with children’s brains, but they did cause cancer due to all that exhaust permeating the air with silent, debilitating, and sometimes carcinogenic fumes.
Octane causes fuel to burn at a predetermined rate. An octane enhancer discourages unwarranted and unwanted explosions. Knowing how long it takes a flame front to travel across a combustion chamber, thanks to controlling octane, allows the engine designer and tuner alike to advance ignition timing or retard it as needed for maximum power output. The spark can ignite the fuel at the most auspicious time for maximum fuel burn, known as the percentage of burn, thus creating the maximum amount of heat.
Some of the main factors determining ignition timing are the gasoline’s rate of burn, piston speed, cylinder diameter, cam timing (when the valves open and close), and whether the engine has dual or single spark plugs per cylinder. The complex blueprint of valves opening and closing on previous and succeeding engine strokes and the spark ignition occurring before the piston (on its compression stroke) reaches the top of its stroke (TDC) is all about combustion lag. Combustion lag is what determines when the spark plug must fire to produce the maximum amount of heat/pressure to drive the piston down on its power stroke.
Gasoline Additive MTBE
The Harley-Davidson M-1063A Safety Recall, Code 088, from November 1, 1996, affected all 1994 FLT/FLHT models, as well as carbureted 1995-97 FLT/FLHT, Softail, Dyna, and Sportster models using vacuum-operated gas petcocks/fuel valves (#61338-94, #61338-94A, and #62169-95). This particular recall did not affect any EFI (electronic fuel injection) Harley-Davidsons. Only a few FLT/FLHT models were fitted with EFI during these years: the FLTCUI, FLHTCI, FLHTCUI, and FLHRI.
The precautionary recall affected bikes and parts manufactured through the end of September 1996. Possibly also those from July and August, but certainly Harley-Davidsons manufactured in September 1996 were classified as early 1997 models and sold as such until midyear 1997 production began. The recall concerns itself with the possible effect of gasoline on the carburetor if you use reformulated gasoline (RFG) containing methyl tertiary-butyl ether (MTBE aka C5H12O), which burns cleaner than regular pump gasoline, or start your H-D without turning the petcock to the ON position. The problem occurs with MTBE contact in RFG gasoline with the petcock’s rubber diaphragm causing it to distort, thus causing fuel flow into the carburetor float bowl to become unpredictable. This could include gasoline supply interruption, which would cause your bike to stop running, possibly in less than auspicious circumstances. The recall did not affect manual petcocks in use before 1994 because they do not have rubber components like a diaphragm.
MTBE has been used in low levels since 1979 to replace lead as an effective octane enhancer, but also a dirty, unhealthy additive, which is okay for your Harley-Davidson. In 1992, in response to the 1990 Clean Air Act Amendments by Congress, the use of MTBE has increased in concentration in some gasolines. This oxygenate compound is produced by methanol reacting with isobutylene. MTBE raises the O2 content of gasoline, which will make it burn better. O2 assists the gasoline in burning more completely, both producing more energy and reducing harmful emissions. Sulfur content in gasoline is a big problem because of its polluting nature, as is benzene, an aromatic, which is another type of oxygenate. Benzene is not healthy for humans. The oxygen in MTBE dilutes or replaces sulfur and benzene content. MTBE is flammable and volatile, and will mix easily with water that gets pumped into a gas tank from the gas station reservoir. This is a good thing, since moisture will burn off. However, it can have an adverse effect on certain rubber compounds like those used in Harley-Davidson Evolution motorcycles, particularly manifold rubbers, rubber carburetor parts, and the rubber used in the diaphragm of the vacuum-operated petcock.
Article continues in next thread. Check back issue for extra information and photos. |
Linear Mode
