With the price we pay for gasoline today, you would expect that the fuel would be far better than back when it was about a quarter per gallon. But such is not necessarily the case. There are many more additives now, which are designed to change the rate of evaporation and burn more cleanly, but they also leave more residues and corrosion in their wake.

If you didn’t heed my advice in the last issue about topping off your tank and adding a fuel stabilizer before storing your motorcycle for the winter, you may be in for an unpleasant surprise this spring. Often, the engine won’t start or will be very difficult to do so, and it may only continue running if the choke is used.

Gasoline is composed of a mixture of “fractions” that have different properties. The lighter portions vaporize easily, and as gasoline ages in storage, these evaporate first. In the early stages of deterioration the engine can still start but may stumble until it’s fully warmed up. After a while, the gasoline begins to oxidize and starts to form gum and varnish-like deposits, which clog jets or injectors. Ethanol, which is often added as 10 percent of the mix, also eats away at the fuel system hoses and components from within. It often leaves white “rust” behind that damages the fuel system.

Carbureted engines are more susceptible to this than fuel-injected models because the electronic fuel injection (EFI) systems spray gasoline through injectors under high pressure, while carbs rely on the smaller difference between atmospheric and manifold pressure to atomize the fuel into a combustible gas.

Look into the tank with a small flashlight (drain fuel if necessary) to determine the amount of rust and sediment in the bottom. Smell the fuel. If it has a pungent odor similar to old paint and varnish, it is stale. The fuel system needs to be drained and flushed before attempting to start the engine.

Drain it completely and add some fresh gas along with a cleaning additive. Fuel filters should also be changed, and hoses that have become cracked or brittle should be replaced.

If all else fails and your motorcycle won’t run properly or at all, you may have to clean the fuel system and carburetor(s) or injectors. You can have it done by a pro, or if you possess the skills, you can do it yourself and save money. Fuel injectors are quite expensive, but they can usually be cleaned out by a shop using special equipment. Use a search engine, such as Google, and look for “fuel injection cleaning service.”

Gasoline presents a fire danger. Avoid sources of ignition, and work outdoors when handling fuel. Wear eye protection, and have a fire extinguisher on hand. Never siphon fuel by sucking on a hose.

Service instructions for every make and model are beyond the scope of this article. Obtain a repair manual and follow it. Work in a large metal pan or tray to contain parts. Service one carburetor at a time, and take photos as you disassemble everything. Check diaphragms for cracks, and ensure the slides and linkage work freely. You can disassemble the carb completely and dip it in a can of carburetor cleaner, or clean the parts with carb cleaner spray and remove the jets. Then boil them in water to remove gum. Make sure all passages are completely clean by looking through them. Stubborn clogs can be eliminated with very thin wire. Replace any seals and gaskets as needed, and reassemble the parts carefully. Check that the throttle linkage works freely and returns to idle. Carburetors may need adjustment, and multiple carbs may require balancing afterward.

Text and Photography: Ken Freund