Modern fuels contain varying amounts of ethanol, whether in E10 unleaded petrol or E85 flex fuel. Many classic car owners equipped with a Weber carburetor wonder whether these fuels are compatible with their fuel system. In this guide, we explain the compatibility of Weber carburetors with ethanol, the precautions to take during long-term storage, and the differences between older and modern Weber carburetors.
Are Weber carburetors compatible with ethanol?
The answer is yes. Genuine Weber carburetors manufactured in Spain are fully compatible with ethanol-blended fuels. Current production models are manufactured using ethanol-resistant materials and are tested with pure ethanol (E100) during development.
Why Can Ethanol Cause Problems?
While the carburetor itself is compatible with ethanol, the properties of the fuel can create issues if a vehicle is left unused for an extended period.
Ethanol is hygroscopic, meaning it naturally absorbs moisture from the air. When fuel remains inside a carburetor for several weeks or months, this absorbed moisture can promote oxidation and corrosion of internal components.
As the fuel evaporates, it can also leave behind deposits that clog small passages, idle jets, main jets, and emulsion tubes, affecting the carburetor's performance.
A Typical Example
The photo below shows the jets and emulsion tube from a Weber 32/34 DMTL after approximately six months of storage with ethanol-blended fuel left inside the carburetor.
When the engine was restarted, it would no longer idle correctly because corrosion and fuel deposits had partially blocked the idle circuit.
The image clearly shows the residue left behind after the fuel evaporated, along with oxidation caused by moisture absorbed by the ethanol.
Regular Use Prevents Most Problems
If your vehicle is driven regularly, fresh fuel continually replaces the old fuel inside the carburetor, making these issues very unlikely.
However, if your vehicle is going to be stored for several months—for winter storage, restoration, or long-term parking—it is good practice to:
- Drain the carburetor float chambers.
- Run the engine until the carburetor is empty of fuel.
- Drain the fuel system before long-term storage whenever possible.
These simple precautions greatly reduce the risk of internal corrosion and clogged jets when the vehicle is returned to service.
Older vs. Modern Weber Carburetors
Weber carburetors manufactured after 2005 are built with seals, diaphragms, and materials that are fully compatible with modern ethanol-blended fuels. These carburetors are validated for use with fuels containing up to 100% ethanol (E100).
For Weber carburetors manufactured before 2005, the carburetor body itself is generally unaffected by ethanol. However, some rubber components—including gaskets, diaphragms, O-rings, and in some cases needle valves—may not have been designed for today's fuels.
The solution is straightforward: during a rebuild, simply replace these components with modern ethanol-compatible parts using one of our Weber rebuild kits. Once refurbished with the correct materials, your carburetor will be fully suitable for use with today's ethanol-blended fuels.
In Summary
Genuine Weber carburetors are compatible with ethanol-blended fuels, provided that older models have been rebuilt using modern ethanol-resistant seals and diaphragms.
The biggest concern is not the carburetor itself, but the effect of leaving ethanol-containing fuel inside it during long periods of storage. With regular use—or by draining the carburetor before long-term storage—you can prevent corrosion, avoid blocked jets, and keep your Weber carburetor performing reliably for many years.
PAFClassic – Your Weber DCOE Specialist
PAFClassic is an official distributor of WEBER Carburettors and WEBCON products.
All carburettors supplied are genuine WEBER carburettors, manufactured in the licensed production facility in Spain under Magneti Marelli licensing.
With access to more than 11,000 carburettor and spare part references, along with WEBER technical documentation, PAFClassic can help identify the correct components for your carburettor.
Beware of counterfeit WEBER carburettors available on the market. Although often sold at attractive prices, they may suffer from lower manufacturing quality, incorrect tolerances, compatibility issues with genuine WEBER parts, difficult tuning caused by inaccurate jet dimensions
For accurate and reliable engine tuning, always choose genuine WEBER components.
