Keihin FCR-MX Carb Rebuild Kit: Contents, Fitment and Options
TOKYOMODS / FCR-MX REBUILD KITS
A good FCR-MX rebuild restores the carburetor's condition and gives you a sound starting point for tuning.
The right kit supplies the service parts your carburetor needs. Choosing it starts with identifying the installed carburetor, inspecting its condition and deciding whether the slide plate or other components also need replacement.
Tokyomods offers two FCR-MX rebuild-kit options: the 98-022 seal and service kit and the 98-025 kit with a billet slide plate. Here is how to compare them and plan the rest of the job.
Which Tokyomods FCR-MX rebuild kit should you choose?
Both options cover multiple sealing areas and include an accelerator-pump diaphragm and screw hardware. The main purchasing distinction is whether you also want the billet slide plate.
| Kit | Listed scope | When to consider it |
|---|---|---|
| Complete FCR-MX Carb Rebuild Kit SKU 98-022 | O-rings and seals, pump diaphragm and carburetor screw kit. | You need a thorough sealing refresh and inspection confirms the existing slide plate is serviceable. |
| Rebuild Kit with Billet Slide Plate SKU 98-025 | The listed seal, diaphragm and hardware package, plus a billet slide plate. | Slide-plate replacement is part of the planned rebuild. |
For a focused slide-plate repair, Tokyomods also offers a separate Billet Slide Plate & O-Ring Kit. Choose between an individual repair and a broader refresh based on inspection findings.
Confirm the carburetor before ordering
The FCR-MX is an off-road development within Keihin's FCR family. It uses a mechanically operated flat slide and accelerator pump, but the FCR name alone does not establish which rebuild parts fit.
Record the bike or ATV's exact year and model, the carburetor's identification markings and its documented bore size. Include clear photos if its history is uncertain. A previous owner may have installed a different carburetor, so the original vehicle application is only useful when it still matches the hardware.
The 98-025 listing names 37, 39, 40 and 41 mm FCR-MX applications and requests the bike's year and model in the checkout notes. Check the current fitment information for the specific kit you are buying. Coverage shown for an individual slide plate should not be transferred to an entire rebuild kit.
If identification is unclear, contact Tokyomods with the markings and photos before ordering. A body-style nickname or a visual resemblance is not enough to establish compatibility.
What is included in the FCR-MX rebuild kits?
The two kit listings cover the following service areas. This grouping makes it easier to compare their contents with the work you have planned:
| Service area | Included components |
|---|---|
| Carburetor body and covers | O-rings for the mid-body, venturi ring and top cover. |
| Fuel inlet and bowl | O-rings for the fuel joint, float bowl, bowl drain and valve seat. |
| Accelerator pump | Diaphragm, U-ring and O-ring. |
| Adjustment, slide and sensor areas | O-rings for the fuel screw, slide plate and throttle position sensor (TPS). |
| Fasteners | Carburetor screw kit. |
The billet slide plate is the additional component in 98-025. Neither listing identifies jets, a jet needle, a float valve or a complete throttle-slide assembly as included components. Account for those separately if your inspection calls for them.
Three names that are easy to confuse
- Valve-seat O-ring versus float valve: the O-ring seals around the seat. The float valve is the separate moving component that works with the float to control fuel entering the bowl. Replacing the seal does not replace a worn valve tip.
- Slide-plate seal versus slide plate: the seal and metal plate are separate pieces. A new seal cannot repair damage to the plate or the rest of the throttle slide.
- Fuel-screw O-ring versus fuel screw: the seal is only one part of the adjustment assembly. Inspect the screw, spring and washer separately.
The official Keihin FCR-MX exploded view helps distinguish these components. For an original-equipment carburetor, confirm application-specific parts against the vehicle's OEM fiche and service information.
Inspect beyond the seals
A rebuild should address contamination and wear together. Cleaning a passage will not repair a damaged seal, and new seals will not remove deposits elsewhere in the carburetor.
Float, inlet valve and fuel leakage
Identify where fuel is escaping before choosing parts. Leakage at a bowl joint and fuel flowing from an overflow can lead to different repairs. Inspect the relevant sealing surfaces, float movement, valve and seat. Verify float height using the procedure and specification for the exact application.
If the carburetor is actively leaking fuel, stop the engine and shut off the fuel supply where possible. Resolve the leak before running the bike again.
Slide plate, rollers and carburetor body
Inspect the plate and seal alongside the throttle slide, rollers and surrounding surfaces. Cracks, excessive wear, binding or damaged threads require individual attention. A billet plate replaces one component; it cannot restore every worn surface in the assembly.
Accelerator pump and hesitation
The pump adds fuel during throttle opening. A damaged diaphragm or leaking pump seal can affect its operation, but hesitation also has other causes. Check the linkage and fuel passages as well as the diaphragm, then evaluate pump operation using the correct service procedure.
Keep the broader engine condition in view. Intake leaks, restricted fuel delivery or ignition problems can remain after an otherwise successful carburetor rebuild.
Plan the rebuild and check the finished installation
Before disassembly, photograph the carburetor and record its jets, needle code, clip position and existing adjustments. Note the intake, exhaust, engine modifications and fuel being used. This gives you a baseline and helps separate a repair from a later tuning change.
Use the correct service information, compatible cleaning products and an organized work area. Keep small components grouped by assembly. Limit disassembly to the planned repair and applicable service instructions; having a seal in the kit does not mean that assembly must be disturbed. Discuss unfamiliar mid-body or TPS sealing work with an experienced FCR-MX specialist.
After installation, check for fuel leakage, correct hose routing and unrestricted throttle return. Confirm cable free play and the hot-start control where fitted. Once the engine is warm, check idle speed and mixture using the application procedure.
Replacing seals does not automatically require larger jets. Establish a mechanically sound baseline, verify float height and assess the bike under its actual operating conditions before changing calibration.
When professional service makes sense
Tokyomods' carburetor service includes disassembly, cleaning, inspection and setup for your application. It is a useful option when the carburetor's history is unknown, internal sealing work is needed, or previous repairs have not resolved the problem.
Use the carburetor service form to provide the bike details, modifications, fuel and running symptoms. Confirm the service scope, any additional parts and current shipping instructions before sending your carburetor.
Common FCR-MX rebuild-kit questions
Will a rebuild kit fix bogging?
It can help when the cause is a component the kit replaces. Identify whether the problem occurs during a quick throttle opening, steady running or another condition, then inspect the relevant systems. A kit purchase alone does not establish the cause.
Should I replace every jet during a rebuild?
Inspect and clean the installed metering parts. Replace damaged or unsuitable components, and preserve the correct jet series and size when restoring an established setup. A routine rebuild does not require an arbitrary change in jet sizes.
How often does an FCR-MX need rebuilding?
Use the vehicle's maintenance guidance and inspection findings. Storage, fuel condition, use and previous maintenance all affect service needs. There is no single mileage or engine-hour interval that suits every FCR-MX application.
Build a complete plan for your FCR-MX
Start with the carburetor identification and inspection findings. Tokyomods can help you choose a rebuild kit, select additional parts or arrange professional service for your application.