Carburetor Kit - CRF250R - 2004 - Repair and Tuning

The Keyster FH-8079N Carburetor Repair and Tuning Kit is designed for the original Keihin FCR01A carburetor used on the 2004 Honda CRF250R. It combines the primary gaskets, float-valve and adjustment components needed for carburetor service with a broad selection of main jets, slow jets and D544-series jet needles for tuning after the carburetor has been returned to proper mechanical condition.

The 2004 Honda CRF250R uses a single carburetor, so Qty 1 FH-8079N kit services the complete original carburetor assembly.

Honda CRF250R Fitment

• 2004 Honda CRF250R

Keihin FCR01A Carburetor

Honda identifies the original 2004 CRF250R carburetor as the Keihin FCR01A. This competition carburetor uses a mechanically operated throttle valve along with an accelerator-pump circuit, hot-start circuit and multiple fuel- and air-metering jets.

Because several circuits overlap throughout the throttle range, correct tuning depends on more than the main jet alone. The slow jet, pilot screw, jet needle, slow-air jet, starter jet and accelerator-pump system all need to be clean and functioning correctly before final jetting decisions are made.

Keyster FH-8079N Kit Contents

• Float Chamber Gasket
• Top Cover Gasket
• #39 Pilot / Slow Jet
• #40 Pilot / Slow Jet
• #42 Pilot / Slow Jet
• #153 Main Jet
• #156 Main Jet
• #160 Main Jet
• #164 Main Jet
• #169 Main Jet
• #174 Main Jet
• D544-L Jet Needle
• D544-S Jet Needle
• D544-R Jet Needle
• D544-RR Jet Needle
• #100 Slow Air Jet
• #68 Starter Jet
• Float Needle Valve
• Pilot Screw
• Pilot Screw Spring
• Pilot Screw Washer
• Pilot Screw O-Ring
• Needle Jet Holder
• Additional O-Ring
• 4 E-Clips

Repair and Tuning Jet Selection

FH-8079N is a repair-and-tuning kit rather than a basic fixed-jet carburetor rebuild kit. It supplies several fuel-metering options around the original CRF250R configuration so the carburetor can be serviced and then adjusted for changes in temperature, elevation, engine setup and competition conditions.

• Main Jets: #153, #156, #160, #164, #169 and #174
• Pilot / Slow Jets: #39, #40 and #42
• Jet Needles: D544-L, D544-S, D544-R and D544-RR
• Slow Air Jet: #100
• Starter Jet: #68

The supplied sizes are tuning options rather than a recommendation to install the richest available combination. Begin from a known baseline and change one variable at a time whenever practical.

Factory 2004 CRF250R Carburetor Baseline

Honda specifies the following standard settings for the 2004 CRF250R FCR01A carburetor:

• Main Jet: #160
• Slow Jet: #40
• Jet Needle: NCYR
• Needle Clip Position: 4th groove from the top
• Pilot Screw: 2-1/4 turns out
• Float Level: 8.0mm
• Slow Air Jet: #100
• Leak Jet: #70
• Starter Jet: #68

The Keyster FH-8079N kit includes jet sizes corresponding to several of these factory reference settings, including the #160 main, #40 slow, #100 slow-air and #68 starter jets.

Before disassembly, record every component currently installed in the carburetor. The CRF250R is a competition motorcycle and many examples have been re-jetted during their service life.

Main Jet Tuning

The main jet has its greatest influence from larger throttle openings through full throttle. FH-8079N supplies six main jets ranging from #153 through #174, with the factory-numbered #160 included in the assortment.

The #156 and #164 selections provide tuning steps immediately below and above the stock-numbered #160 reference, while #153, #169 and #174 extend the available adjustment range.

Temperature, elevation, engine condition and intake or exhaust modifications can all affect the required mixture. Do not assume that a modified motorcycle automatically requires the largest supplied main jet.

Pilot / Slow Jet Tuning

The slow jet and pilot screw strongly influence starting, idle and small throttle openings. FH-8079N includes #39, #40 and #42 slow jets, placing the factory #40 size in the middle of the supplied tuning range.

Honda specifies an initial pilot-screw setting of 2-1/4 turns out for the stock 2004 configuration. This provides a useful starting reference after the carburetor has been cleaned and rebuilt.

Before changing slow-jet size, make sure the pilot passages are completely clean and the intake system has no air leaks. A blocked passage or mechanical problem should not be compensated for with richer jetting.

D544 Jet Needle Selection

The kit includes four Keyster D544-series tuning needles: D544-L, D544-S, D544-R and D544-RR. These provide alternate fuel-metering profiles through the part-throttle range.

Honda's original standard needle is the NCYR installed in the fourth groove from the top. The D544-series needles are tuning alternatives and should not be treated as four identical replacements for the original Honda NCYR calibration.

If the motorcycle still has its original NCYR needle, retain it during the rebuild so the carburetor can be returned to the known factory baseline if needed.

#100 Slow Air Jet

The FCR01A uses a #100 slow-air jet as part of the low-speed metering system. FH-8079N includes a replacement #100 slow-air jet.

The air jet works together with the fuel side of the slow circuit, so both the air passage and the fuel passages must be clean before pilot-circuit tuning is evaluated.

#68 Starter Jet

The starter circuit supplies additional fuel for cold starting. Honda specifies a #68 starter jet for the original 2004 CRF250R carburetor, and FH-8079N includes a #68 replacement.

Clean the starter circuit and inspect the choke and hot-start systems during carburetor service. Starting problems should not automatically be attributed to the main or slow jet.

Important #70 Leak Jet Note

The 2004 CRF250R FCR01A carburetor uses a #70 leak jet as part of the accelerator-pump circuit. The leak jet controls how much accelerator-pump fuel is bypassed back into the float chamber and therefore influences the pump shot during rapid throttle opening.

FH-8079N does not include the #70 leak jet. Inspect and clean the existing leak jet during service and retain it unless a separate replacement or deliberate accelerator-pump tuning change is required.

Float Needle Valve and Fuel Level

The supplied float needle valve controls fuel entering the float chamber. A worn or contaminated valve can contribute to flooding, fuel leakage, inconsistent fuel level or difficult starting.

Honda specifies an 8.0mm float level for the standard 2004 FCR01A setup. After installing the replacement valve, inspect float movement and verify the float level before final carburetor tuning.

Honda OEM Cross-References

Several FH-8079N components correspond with original Honda parts used in the 2004 CRF250R FCR01A carburetor:

• 16100-KRN-671: FCR01A A Carburetor Assembly
• 16010-KRN-671: Carburetor Gasket Set
• 16011-KZ3-J11: Float Valve Set
• 16014-KRN-671 / 16014-KRN-731: Carburetor Top Set references
• 16016-MEB-671: Screw Set A / Pilot Screw Components
• 16163-MEB-671: Float Chamber Gasket
• 16165-MEB-671: Needle Jet Holder
• 16203-MEN-671: NCYR Jet Needle Set
• 99113-GHB-1600: #160 Main Jet
• 99103-GBF-0400: #40 Slow Jet
• 99104-MEB-1000: #100 Slow Air Jet
• 99108-KRN-0700: #70 Leak Jet
• 99112-KRN-0680: #68 Starter Jet

These Honda OEM numbers are provided for component identification and cross-reference purposes. FH-8079N contains Keyster replacement and tuning components rather than Honda-branded OEM parts, and its alternate D544 needles and tuning jets should not automatically be assumed to duplicate Honda's optional jetting calibrations.

Float Chamber and Top Cover Gaskets

The float chamber and upper carburetor cover are opened during major FCR service. Their seals can harden, shrink, flatten or tear after repeated heat cycles, fuel exposure and previous disassembly.

Clean all gasket grooves and mating surfaces carefully before installing the replacement components. Avoid damaging the aluminum sealing surfaces with aggressive scraping tools.

Pilot Screw Components

FH-8079N includes a replacement pilot screw, spring, washer and O-ring. These components are important to accurate low-speed mixture adjustment and are easily damaged or lost during previous servicing.

Never force the pilot screw tightly against its seat. Turn it inward only until lightly seated before establishing the baseline opening.

Clean the Accelerator-Pump and Fuel Circuits Before Tuning

The FCR01A contains more fuel-metering circuits than a simple conventional carburetor, so thorough cleaning is especially important. Inspect and clean the main, slow, slow-air, starter, leak-jet, needle and accelerator-pump passages before tuning.

A jetting change cannot correctly compensate for a blocked passage, damaged accelerator-pump component, incorrect float level, intake leak or contaminated fuel system.

One Kit Services the Complete CRF250R Carburetor

Keyster FH-8079N services one carburetor. Because the 2004 Honda CRF250R uses a single Keihin FCR01A carburetor, Qty 1 kit is required for a complete carburetor rebuild and tuning setup.

Important Installation and Tuning Notes

• One kit services one carburetor; Qty 1 services the complete original CRF250R carburetor.
• Keyster reference FH-8079N.
• Fits 2004 Honda CRF250R.
• Designed for the original Keihin FCR01A carburetor.
• Factory baseline is #160 main, #40 slow and NCYR needle in the 4th groove.
• Factory pilot-screw baseline is 2-1/4 turns out.
• Factory float level is 8.0mm.
• Includes six tuning main jets: #153, #156, #160, #164, #169 and #174.
• Includes three slow jets: #39, #40 and #42.
• Includes four D544-series tuning needles: D544-L, D544-S, D544-R and D544-RR.
• Includes #100 slow-air and #68 starter jets.
• The original #70 leak jet is not included; inspect and retain or replace separately as needed.
• Retain the original NCYR needle if returning to the factory calibration may be necessary.
• Record all existing carburetor settings before making changes.
• Change one tuning variable at a time whenever practical.
• Verify accelerator-pump operation, float level and all fuel/air passages before final tuning.