The fuel available at UK forecourts today is significantly different from the petrol that classic motorcycles were designed to run on. The introduction of ethanol blending — now mandated at a minimum of 10 percent (E10) at most filling stations — has created challenges for owners of older machines, and understanding what this means in practice is important for every classic rider.
What Is E10 Fuel?
E10 is petrol blended with up to 10 percent bioethanol. It was introduced across the UK in 2021 to reduce carbon emissions from road transport. While modern vehicles are designed to run on E10 without modification, many classic motorcycles — particularly those produced before the late 1980s — have components that are not compatible with ethanol-blended fuel.
The Problem with Ethanol
Ethanol is hygroscopic — it absorbs moisture from the atmosphere. In a carburettor or fuel system left with ethanol-blended fuel for an extended period, this moisture absorption can lead to corrosion of metal components, degradation of rubber seals and fuel lines, and the formation of gummy deposits that block jets and passages. For machines used infrequently and stored between outings, this is a significant concern.
E5 Super Unleaded: The Classic Owner’s Friend
E5 super unleaded — available at most UK filling stations — retains a maximum ethanol content of 5 percent and is the recommended fuel for classic and vintage vehicles not compatible with E10. While it carries a price premium over standard unleaded, the protection it offers to older fuel systems makes it the correct choice for classic motorcycles.
Fuel Stabilisers and Carburettor Care
For machines that will be unused for more than a few weeks, a quality fuel stabiliser used in conjunction with E5 super unleaded provides additional protection against fuel degradation. Draining the carburettor before extended storage remains the most reliable prevention against ethanol-related deposits.
For advice on fuel and fuel system care for your classic, contact South Wales Classic Motorbikes on 07966 296269 or visit southwalesclassicbikes.com.