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Fuel - FADM Stern GNSF

These bikes will run on most grades of gasoline available, with the grade type being a matter of personal preference. While these bikes will run quite fine on standard 87 octane gas, some prefer higher octane gas, like 91. While some engines may not show any difference in performance, some may, but either way it won't hurt the engine (just the wallet).


Gasoline is actually a blend of many different petroleum products based on the type and rating of the gasoline. Some countries have "summer" and "winter" grades of gas, with the summer one being less volatile. Along with the petroleum products used to make the gasoline, there are many additives that are also included, one being ethanol. Along with all the volatile components in gasoline, there is a small percentage of "suspended solids" present (gums) which all have probably seen when cleaning a carburetor. These solids are usually carried through the fuel system and sent out the exhaust system during normal engine operation, but if the fuel is allowed to sit for a long period of time, they will come out of suspension and form deposits as the volatile components evaporate.

Octane Rating

The octane number (or Anti-knock index) for gasoline indicates the concentration of "octane" (2,2,4-trimethylpentane) in that mixture. The higher the octane number, the less susceptible the fuel is to "self ignition" while being compressed. A higher octane rating allows a higher compression ratio, and thus higher temperatures and pressures, which translate to higher power output. This is important in high performance engines, but in our engines, 87 octane is more than sufficient.

Ethanol In Gasoline

With current day refining of gasolines and laws, most are now being made with a percentage of ethanol (ethyl alcohol) added up to a limit of 10% (E10). It is added mainly as a way to decrease CO (Carbon Monoxide) emissions into the atmosphere. While it functions well for this purpose, it can degrade rubber and plastic parts within an engine if those parts weren't designed to withstand ethanol-blended gasolines. It also has another negative quality, which is its affinity for water. This results in the ethanol "pulling in" and dissolving water (from the air) into the fuel.


There are many additives that can be added to gasoline to improve longevity of the fuel, improve the octane rating, and help keep the fuel system clean. Some of these categories are;

    • Anti-knock

Lead was used as an anti-knock additive in the past (leaded gasoline) but has since been banned from use. Methylcyclopentadienylmanganese tricarbonyl (MMT) has been used for many years in Canada and recently in Australia to boost octane. It also helps old engines designed for leaded fuel run on unleaded fuel without need for additives to prevent valve problems.

    • Stabilizers

Fuel degradation can be slowed dramatically through the addition of antioxidants, such as phenylenediamines and other amines, unhindered or partially hindered phenols and oil-soluble strong amine bases, such as hindered phenols (like Seafoam). Gasolines are also treated with metal deactivators, which are compounds that sequester (deactivate) metal salts that otherwise accelerate the formation of gummy residues. The metal impurities might arise from the engine itself or as contaminants in the fuel.

    • Detergents

Gasoline, as delivered at the pump, also contains additives to reduce internal engine carbon buildups, improve combustion, and to allow easier starting in cold climates. Typical detergents include alkyl amines and alkyl phosphates.

    • Ethanol

In most states, ethanol is added by law to a minimum level which is currently 5.9%. Most fuel pumps display a sticker stating the fuel may contain up to 10% ethanol (E10), an intentional disparity which allows the minimum level to be raised over time without requiring modification of the literature/labelling. The main reason is that ethanol is an oxygen-bearing compound (oxygenates). The presence of these oxygenates reduces the amount of carbon monoxide and unburned fuel in the exhaust gas. In many areas throughout the US, oxygenate blending is mandated by EPA regulations to reduce smog and other airborne pollutants. For example, in Southern California, fuel must contain 2% oxygen by weight, resulting in a mixture of 5.6% ethanol in gasoline.


Due to the makeup of gasoline, most of its components are considered "volatile," meaning they vaporize easily and have a high "Vapor Pressure" (at a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure). Since the many compounds in gasoline all have different vapor pressures, when gas is sitting some will vaporize (evaporate) faster than others. When this happens the percentages of some of the compounds that make up the gasoline go down, resulting a less efficient fuel (stale gas).

Stabilizing for Storage

If fuel is to be stored for a long time, steps must be taken to reduce the degradation of the fuel caused by vaporizing and oxidation. As gasoline sits open to the air (remember, the gas cap DOES vent to the outside world) two things happen to it. First, the volatile components evaporate out of the liquid (vaporize) and reduce their percentages in the fuel. Also, the fuel undergoes "oxidation" while in the presence of air.

Good quality gasoline should be stable almost indefinitely if stored properly. Such storage should be in an airtight container, to prevent oxidation or water vapors mixing, and at a stable cool temperature, to reduce the chance of the container leaking. When gasoline is not stored correctly, gums and solids may accumulate resulting in "stale fuel". The presence of these degradation products in fuel tank, lines, and carburetor make it harder to start the engine. Upon the resumption of regular vehicle usage, though, the buildups should eventually be cleaned up by the flow of fresh Fuel, except in cases where small passages get plugged with gum (like carburetor jets and fuel filter mesh screens). Fuel stabilizers can be used to extend the life of the fuel that is not or cannot be stored properly. Users have been advised to keep gasoline containers and tanks more than half full and properly capped to reduce air exposure, to avoid storage at high temperatures, to run an engine for ten minutes to circulate the stabilizer through all components prior to storage, and to run the engine at intervals to purge stale fuel from the carburetor.

To store your bike, a few simple things can help keep the gas from degrading, such as;

  • Make sure the tank is filled before storage
  • Use cling wrap or similar to seal the gas cap so that is no longer venter to the air
  • Add a stabilizer to the fuel before storing the bike
  • Run the carburetors dry (or remove fuel from float bowls)
  • "Fog" the engine with an appropriate product

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