This article concludes in this thread.
There are various trains of thought about fuel tank storage. The first methodology works well from an internal fuel tank protection perspective. The main recommendation in some manuals is to fill the fuel tanks using equal amounts of gasoline and oil in a mixture. I find this labor intensive and potentially messy. Furthermore, storage and disposal of the oily gas is necessary afterward when putting in fresh gasoline. Running the oil-fuel mixture through the bike will produce noxious emissions, and, from a practical standpoint, may foul the spark plugs, preventing spark arcing across the electrodes, thus preventing engine operation.
I’ve always stored my bikes with a full tank of gasoline to prevent oxidation and condensation. Condensation will cause oxidation, as well as other chemical reactions that will compromise the integrity of the tank itself and pollute gas flow into the induction system. If the pollutants get through the carburetor or EFI components without disturbing their various internal functions (float needle setting and plugging jets, orifices, or injectors) they will most times burn in the combustion chamber.
Gasoline may separate over time if it has an ethanol or other oxygenate components. It may be advisable to add a gasoline stabilizer to a full tank of gas for storage. I’ve never done this, and have yet to have a bad experience, but that does not mean it cannot happen. If the bike runs rough after bringing it out of storage, the worst that happens is the gasoline needs to be changed. The rider can even get away with riding the bike, using up some fuel, and topping up with fresh gas until the problem disappears.
Leaving a full tank of fuel for a few weeks or months will come with its own risks. This quantity of gasoline is heavy, so that pressure will be put on the gas petcock, which controls the gas in a gravity-feeding system. It’s essential that the carbureted petcock, whether manually activated or vacuum-operated, be in good working order to seal the gas in the tank.
Many manuals advise draining the tank(s) and spraying (defogging or fogging) a rust inhibitor onto the insides of the tank(s). To me, this is just more work and expense. The bike may run rough for awhile after being taken out of storage and refilling the gas tank. There are many commercially available inhibitors. If nervous, purchase one from your local dealer or aftermarket shop. Follow the manufacturer’s instructions.
The reader can make up his mind on the best methodology for him. Many riders like to do what their dealer recommends to avoid warranty hassles and the “I told you so” put-down lectures. However, some bike shops, dealers or otherwise, will recommend a methodology that will allow them to sell you a product or service. Personally, I check the integrity of the petcock, and then just fill the tank and leave it. Worst case scenario at the end of the day is that I may have to run some fresh gas through my bike after initial start-up.
One last thing that you should do is to drain the carburetor float bowl. With the petcock in the Off position, loosen the fuel bowl drain screw (bolt) a full turn to allow the float gasoline to drain away into a container. Retighten the float bowl drain screw (bolt). Do I do this? No, I don’t. Occasionally, I have run across bikes where the gas has formed a white powder in the float, but my experience is that it dissolves with fresh gas once the petcock is turned on. Again, the bike may run rough for a minute or two, but should straighten itself out. If not, flush the float and jets with gas. However, just because I can be a lazy (or is that prudent?) person and avoid work that some feel necessary does not mean that you have to. I just do what has worked for me over time. When I find a reason to do work, I will be the first at it.
The very last thing to remember is not to store the bike near open flames like pilot lights, especially in enclosed spaces without air circulation. Use common sense.
Evaporate Gas
Gasoline evaporates naturally and easily into the air. A good fuel has this quality. It also makes it an environmental pollutant and thus a target of the EPA and CARB (California Air Resources Board) environmental regulatory agencies.
Harley-Davidsons have had a vent hole in the gas cap forever. Older gas caps had a two-way venting system, which is just a hole whereby air could travel into the tank to fill space left by the vacating gas. The gas cap vent also allowed evaporating fuel to vent out into the atmosphere. Only one situation exists at a time, since evaporative build-up will fill the void of draining gas, and its pressure will even assist by pushing gas out of the tank that normally exits via the force of gravity. Therefore, a build-up of evaporate gas will preclude the need for air to vent into the tank to fill the void of exiting fuel.
Modern Harley gas caps also vent, but only one way. They allow air in as gas drains into the induction system, whether it is a carburetor or electronic fuel injection. Gas cannot flow out of the tank if a vacuum is created in the space it vacates. This is why air must vent in.
Later caps prevent vapors from venting out through the gas cap. These vapors feed back to a vapor valve in a basic way. Some aftermarket gas tanks, like most Sporty and Softail replicas, have a standpipe. This metal tube runs inside the gas tank from the gas cap bung/tank down to an outlet at the bottom of the tank. Some stock H-D tanks generally have the vent (standpipe outlet) underneath the dash panel. I have never liked this system because it is too close to the electrics, like the wiring and ignition switch. Electrical shorts and gasoline vapors can have very explosive relationships. Other models will have the standpipe in a safer place. Follow any small tubing around the gas tank, and it will invariably lead to a gizmo called the vapor valve at one end and the fuel tank standpipe at the other.
An evaporative vapor standpipe may exit the tank at or near the bottom. Do not let this fool you, as there will be an internal pipe going up above the gasoline’s highest level. The gas cap screws into the gas cap bung. The portion that the standpipe connects to is always above the gasoline level inside the tank, no matter how much fuel is in the tank. A rubber line connects to the outlet at the bottom of the tank, under the dash, or elsewhere, as the case may be, and routes to a vapor valve (#62150-85) on 1985 and later rubber-mounted FLTs, FLHTs, FXRs, and 1991-98 Evolution Dynas. The vapor valve continues to be used with all the Twin Cam models. Resurrected Screamin’ Eagle Evolution FXRs in 1999 and 2000 also use this methodology. Softails use the same vapor valve from 1985-99 as Evolutions, as do the 2000 to present Twin Cams.
The vapor valve is usually located near the center frame downtube if on a Softail. Rubber-mounted Dynas and FLT models don’t have a frame downtube, but the vapor valve is generally on the frame body where it angles back and down to the rear of the gas tank. On some models the vapor valve clips to the frame member immediately in front of the fuel tank. Different years and models place the vapor valve in convenient locations. Follow the vent line away from the fuel tank to find the small black plastic vapor valve. The rubber-mounted models, particularly later year ones, may have a fitting on the gas cap bung above the tank on the outside. A fuel door or a gas tank shield covers the raised gas cap bung with these tanks. A rubber hose will connect to this fitting. It then runs back and connects to the top of the vapor valve.
For safety reasons, if the bike tips over too far beyond the riding lean angle, the vapor valve prevents gasoline from escaping through the vent. Firstly, this keeps an expanding puddle of gas from running onto the ground and evaporating around a hot engine if the bike falls over. Secondly, for environmental and safety reasons it prevents evaporating venting fuel from escaping. A hot engine, exhaust, electrical short, a lit cigarette, or other causes can easily ignite the vapor.
A hose connected to the bottom of the vapor valve directs the fumes away. This hose leading away from the vapor valve routes it downward and vents vapor into the atmosphere above the rear belt on FLT models. Other Harleys have the vent tube attached to a fitting on a frame member.
The evaporated emissions feed inside the frame tubing. They can escape out through open frame ends that are uncapped. The goal is always the same: get the inflammable vapor away from the rider and any engine or exhaust component that has potential to ignite it. As we’ll see in the next issue, California takes this a step further and reingests the fumes back into the engine for combustion.
Conclusion
Next month, we’ll do an in-depth study of California’s CARB EVAP system.
Donny Petersen
Tattoo Tony’s Heavy Duty Cycles
Toronto, Canada
www.HeavyDutyCycles.com 
Techline-Oct09-Evolution Fuel Delivery-Pt I concludes 
Linear Mode
