Classic motorcycles were designed for petrol without ethanol. In much of Europe the standard 95-octane petrol is now E10, which means it contains up to ten percent ethanol. Ethanol is a good fuel component, but it behaves differently from petrol in old fuel systems. Here is what that means and what you can do about it. For a longer treatment, see the blog post what ethanol gasoline actually does to a classic fuel system.
What ethanol does
- It attracts water. Ethanol absorbs moisture from the air. In a bike that stands, the fuel can collect enough water to cause corrosion in the tank, the tap and the carburettors.
- It can attack some old materials. Older rubber, cork, fibre gaskets and some sealants and tank liners can swell, soften or break down in contact with ethanol.
- It can corrode metal. Some die-cast carburettor bodies and aluminium parts corrode, and a white powder inside the carburettor is a sign of it.
- It ages faster. Petrol with ethanol stales sooner, especially when the tank is not full.
Not every bike suffers. Many classics run on E10 for years without a problem. But a bike that is used rarely is most at risk, because the fuel sits for months.
Choosing fuel
- Use petrol with less ethanol where you can. In many countries the 98-octane grade contains no more than 5% ethanol (E5). Check the pump label.
- Ethanol-free fuel. Specialist fuel sold in cans or at some stations has no ethanol. It is expensive, but it stores for years, and some owners use it for storage and for rare bikes.
- Use fuel fresh. Do not keep fuel in the tank for many months. Drain it or add a stabiliser for winter storage. See winter storage.
- Check the octane for your engine. Most classics were built for lower octane than today's fuels.
What to replace
- Fuel hose. Replace old rubber hose with hose labelled for ethanol use. Fit new clips.
- Carburettor O-rings and gaskets. Replace them with ethanol-resistant material such as Viton when you rebuild.
- Floats. Cork or old plastic floats may swell or sink. Brass and modern plastic floats are available for many carburettors.
- Fuel tap. The seals and the strainers in a tap age. A rebuild kit is cheap and available for many types.
- Tank liner. If the tank has a coating that is peeling, remove it and reline with a product made for ethanol. Rust-free metal is better than any liner, so clean the tank if you can.
- Fuel filter. Fit an inline filter if there is none, and check it each season.
Signs of trouble
- White or green powder in the carburettor bowl.
- Black flakes in the fuel, which can be the lining of the hose or the tank.
- A fuel smell, or a wet spot under the tap.
- Hard starting after the bike has stood for a few weeks.
- Swollen or sticky gaskets and O-rings.
Practical routine
- Keep the tank full when the bike is not used for a while.
- Do not leave fuel in the carburettors for a long period. Shut the tap and run the carburettors dry before storage when the manual allows.
- Check the hoses and the tap each spring.
- Replace hoses by age, not just by look.
- Keep a note of what you changed and when.
See also carburettor basics and waking up a bike from storage.
