FKM (Viton) Carburettor Seals: Why We Use Them at The Carb Shack

When it comes to rebuilding motorcycle carburettors, the smallest components can make a significant difference. Seals and O-rings might not be the most exciting parts of a carburettor, but choosing the right materials is essential to producing a reliable, quality rebuild.

At The Carb Shack, we use FKM seals, commonly known by the trade name Viton, in our own carburettor rebuild kits. We believe the quality of the components used during a rebuild matters just as much as the cleaning, preparation and assembly that go into it.

But what exactly are FKM seals, how do they differ from standard rubber seals, and why do we choose them for our motorcycle carburettor rebuilds?

What Are FKM Seals?

FKM is a type of fluorocarbon elastomer designed to provide excellent resistance to many fuels, oils, chemicals and elevated temperatures.

You may also know FKM by the name Viton. Viton is a recognised trade name for a family of fluoroelastomer materials, while FKM is the general material designation.

These materials are widely used in applications where ordinary rubber compounds may struggle to withstand exposure to fuel, oil and heat.

Inside a motorcycle carburettor, seals and O-rings are responsible for maintaining tight sealing between components. Depending on their position, they may be exposed to petrol, vapour, heat and the effects of ageing.

Using an appropriate seal material helps these components perform their intended job throughout the rebuild.

Why Are FKM Seals Important in Motorcycle Carburettors?

Motorcycle carburettors contain numerous small seals and O-rings, including those fitted to fuel connections, fuel rails, mixture screws and other sealing points.

Although these components are small, their condition can have a direct impact on how a carburettor functions.

A seal that has deteriorated, hardened, swollen or lost its ability to seal correctly can contribute to fuel leaks or other carburettor problems, depending on its location.

This is why replacing worn seals is an important part of a proper carburettor rebuild.

However, simply replacing an old seal with a new one is not the whole story. The material needs to be suitable for its intended application.

FKM offers several useful properties that make it an excellent choice for many motorcycle carburettor sealing applications.

1. Resistance to Petrol and Fuel Exposure

One of the main reasons we use FKM seals is their resistance to many hydrocarbon fuels.

Carburettor seals can remain in contact with petrol for extended periods. The wrong elastomer compound may swell, deteriorate or lose its sealing properties when exposed to incompatible fuels.

FKM materials generally provide good resistance to many petrol-related compounds, making them well suited to a range of carburettor applications when the correct grade is selected.

Modern fuel formulations can vary, so no seal material should be assumed to be compatible with every fuel under every condition. Correct material selection remains important.

2. Resistance to Heat

Motorcycle carburettors operate in an environment affected by engine heat, under-bonnet temperatures and heat soak after the engine has been switched off.

FKM is known for its resistance to elevated temperatures compared with many conventional elastomer materials.

This can make it a suitable choice for carburettor seals exposed to demanding operating conditions.

The actual temperature resistance depends on the particular FKM compound and the application, but its heat-resistant properties are one of the reasons it is widely used in automotive and industrial sealing applications.

3. Resistance to Oils and Chemicals

Carburettors are part of a wider mechanical system where oils, fuel residues and other substances may be present.

FKM offers good resistance to many oils and chemicals, helping it maintain its properties in suitable applications.

This versatility is another reason we favour FKM when selecting sealing components for our rebuild kits.

4. Long-Term Sealing Performance

A quality rebuild is about more than making old carburettors look clean. The internal components need to be suitable for continued use.

Choosing an appropriate seal material is one part of achieving that objective.

FKM’s resistance to many fuels, oils and elevated temperatures can help seals retain their useful properties in service. As with any elastomer, actual service life depends on the material grade, installation, operating conditions, fuel compatibility and maintenance.

At The Carb Shack, we want the parts we install to reflect the same attention to detail as the work we carry out.

FKM vs Standard Rubber Carburettor Seals

Not all rubber seals are manufactured from the same material. Different elastomers have different strengths, and the best option depends on the application.

FKM is often selected where fuel resistance, chemical resistance and heat resistance are important considerations.

Standard rubber seals may be perfectly suitable for some applications, but their performance depends on the particular compound being used.

It is important to remember that not every black rubber O-ring is the same. Appearance alone cannot tell you whether a seal is suitable for prolonged fuel exposure.

Equally, FKM is not automatically the right choice for every seal in every mechanical application. Material grade, dimensions and compatibility all matter.

For motorcycle carburettors, we select FKM because its properties suit many of the sealing applications encountered during our rebuild work.

Why We Use FKM Seals in Our Carburettor Rebuild Kits

At The Carb Shack, we specialise in motorcycle carburettor cleaning, rebuilding and restoration.

We work with carburettors from a wide range of manufacturers and motorcycles, from older British & Japanese machines to more modern performance applications.

When developing our own carburettor rebuild kits, we pay attention to the components included and the materials used.

We use FKM seals because we want the components in our kits to reflect the standard of work we carry out in our workshop.

Our approach is not simply to put together a collection of replacement parts and call it a rebuild kit. We want to supply components that are appropriate for their intended application and that we are confident using in our own rebuilds.

That is why FKM seals feature in our own TCS carburettor seal kits.

Whether you are rebuilding a set of carburettors yourself or having them professionally restored, the quality and suitability of the replacement components deserve consideration.

Can You Replace Standard Carburettor O-Rings With FKM Seals?

In many cases, FKM can be an excellent replacement material for carburettor O-rings, provided the seal is correctly specified for the application.

However, choosing a replacement involves more than matching the approximate diameter.

The following factors should be considered:

• Correct dimensions: The internal diameter and cross-section must match the intended sealing position.
• Material compatibility: The FKM compound must be suitable for the fuel and operating conditions involved.
• Correct installation: Seals must be fitted without damage, twisting or pinching.
• Application-specific requirements: Some sealing positions may require a particular material or design.

Using the wrong size or an unsuitable material can lead to sealing problems regardless of how good the material may be in general.

For this reason, we recommend selecting a carburettor seal kit specifically designed for your carburettor model rather than relying on a generic assortment of O-rings.

Why Seal Quality Matters During a Carburettor Rebuild

A carburettor rebuild involves more than removing dirt and replacing a few obvious worn parts.

Depending on the condition of the carburettors and the scope of the work, a rebuild may involve dismantling the assemblies, cleaning internal passages, inspecting components, replacing appropriate seals and other worn parts, checking settings and carrying out relevant leak tests.

Even the best cleaning process cannot compensate for an incorrectly sized seal or a replacement component made from an unsuitable material.

Likewise, fitting quality seals does not eliminate the need for correct assembly, accurate settings and proper testing.

Every part of the process has a role to play.

This is the philosophy behind The Carb Shack: attention to detail throughout the job, from the components selected to the final checks.

Shop FKM Carburettor Seal Kits From The Carb Shack

If you are rebuilding your motorcycle carburettors, choosing the correct seal kit is an important part of the process.

Our TCS carburettor seal kits use FKM (Viton) seals where best suited and are developed for specific applications, helping you source the replacement seals required for your rebuild.

Rather than relying on a universal kit that may not contain the correct parts, choose a kit designed for your particular carburettors.

Browse the available kits on The Carb Shack website to find the right option for your motorcycle.

Browse TCS Carburettor Seal Kits

If you are unsure which kit you need, get in touch with The Carb Shack before ordering. Providing your motorcycle’s make, model and year, along with any relevant carburettor identification, will help us establish which kit is appropriate.

Frequently Asked Questions About FKM Carburettor Seals

Are FKM seals the same as Viton seals?

FKM is the general designation for a family of fluorocarbon elastomers. Viton is a trade name associated with FKM materials. The terms are often used interchangeably in the automotive aftermarket, although individual grades and formulations can differ.

Are FKM seals suitable for petrol?

FKM materials generally offer excellent resistance to many petrol and hydrocarbon fuel formulations. Suitability depends on the specific compound and fuel composition, so compatibility should be confirmed for the intended application.

Are FKM seals better than standard rubber O-rings?

FKM offers advantages in fuel resistance, oil resistance and heat resistance compared with many conventional rubber compounds. However, the best material depends on the application and the properties required.

Why do motorcycle carburettors need replacement seals?

Seals can harden, deteriorate, swell or lose their ability to seal correctly over time. Replacing unsuitable or worn seals during a rebuild can help prevent leaks and restore the intended sealing function.

Do The Carb Shack rebuild kits use Viton seals?

Yes. Our own TCS carburettor seal kits use FKM (Viton) seals, selected as part of our approach to supplying quality replacement components for motorcycle carburettor rebuilds.

Can I fit FKM seals myself?

Yes, if you have the necessary mechanical knowledge, correct tools and an application-specific kit. Take care when removing old seals and fitting replacements, as incorrect installation can damage the seal or its seating surface. Always follow the relevant service information for your carburettors. We recommend using O-Ring Pliers and a small amount of grease or WD40 to help with installation.

The Carb Shack: Quality Starts With the Details

A successful carburettor rebuild depends on getting the details right.

Cleaning, inspection, component selection, assembly and testing all matter. The seals may be small, but they play an important role in the overall result.

At The Carb Shack, we use FKM seals in our own rebuild kits because material quality is an important part of the standard we aim to deliver.

If you are looking for motorcycle carburettor seal kits made with FKM (Viton) seals, explore the range available from The Carb Shack and find the kit designed for your carburettors.