Is petrol damaging my 20-year-old bike?

Q. I’ve just seen an advertisement for a product that will protect motorcycle engines made before 1996 from damage that will, according to them, result from use of petrol containing ethanol.

I have a Honda manufactured in 1991. Could you let me know if this is the case as I don’t want to go buying products if I don’t need them.
Steve Bencher, MCN forums

A. The drive towards biofuels has seen the rise of ethanol, a plant-derived alcohol, in petrol blends and EU legislation has allowed ethanol up to 5% for many years.

In 2007 our government passed the Renewable Transport Fuel Obligation, ramping up ethanol content from 3.25% in 2009/10 to 5% and E5 fuel for 2013/14.

The issues with ethanol are firstly that it is hydroscopic, attracting water molecules, which can build up in fuel tanks and cause corrosion problems, especially if you do not use your bike regularly and the fuel sits there in a damp environment like an unheated garage.

It can also affect some rubbers and plastics and owners of classic bikes have been reporting problems with rubberised fuel tank sealants they applied internally to block up pinholes, then breaking down and getting sucked into the fuel system and buggering up carbs and filters.

Ethanol is also quite a ‘light’ component in a fuel mix, so it evaporates more readily making the fuel less volatile, which means it burns hotter as well as making an engine hard to start.

Again, this shouldn’t be a problem if you use your bike regularly and keep the tank topped up so there isn’t much of an ‘air gap’ in the tank if it is going to standing idle.

An attempt by the German government to up ethanol to 10% was headed off last year by a motorists’ revolt after the likes of BMW and Mercedes refused to guarantee that it wouldn’t affect their vehicles and the fact is that ethanol doesn’t have so much energy, so an E10 fuel would give worse fuel consumption.

A 20-year-old bike like yours should be perfectly alright on E5 fuel as long as you use it regularly.