PROX N424-21 Keihin Pilot Jet #42 Honda CRF150R — main product image

PROX N424-21 Keihin Pilot Jet #42 Honda CRF150R

PROX

PROX N424-21 Keihin Pilot Jet #42 Honda CRF150R

Name: PROX N424-21 Keihin Pilot Jet #42 Honda CRF150R
Brand: PROX
SKU: N424-21

Precision-machined #42 pilot jet for Keihin carburetors that restores crisp throttle response on Honda CRF150R models from 2007–2009.

$17.01*

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*Price sourced from Amazon.com. Last updated:Jul 13, 2026.Price and availability are subject to change.

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Overview

The Pro X N424-21 is a #42 pilot jet machined specifically for Keihin carburetors fitted to Honda CRF150R dirt bikes from model years 2007 through 2009. The pilot jet is one of the smallest but most consequential components in a carburetor's fuel circuit — it governs fuel flow at idle and through the low throttle range, directly affecting how the bike pulls from a stop, idles on the stand, and responds during slow technical riding. A worn, clogged, or incorrectly sized pilot jet shows up immediately as a hesitant or erratic idle, lean stumble off the bottom, or a persistent need to fiddle with the fuel screw to keep the engine happy.

Pro X manufactures this jet to tight tolerances appropriate for Keihin carburetor thread and orifice geometry, meaning it installs cleanly and seals correctly against the float bowl without requiring thread chasing or sealant. The #42 size places it in standard pilot jet territory for the CRF150R application — though riders who have modified intake or exhaust components, or who ride at significantly different altitudes than sea level, should cross-reference this size against their specific tuning needs. Installation is accessible to any rider comfortable pulling a carb off the bike: drain the float bowl, locate the pilot jet on the carb body, swap it with a flat-blade screwdriver, and reassemble. Note that this part is not available to California residents per CARB regulations.

Key Features

This product cannot be sold to residents in the state of California.

High quality aftermarket jets for Keihin carburetors.

Specifications

Brand

Pro X

Part Number

N424-21

Type

Pilot Jet

Jet Size

#42

Carburetor Compatibility

Keihin

Application

Honda CRF150R 2007–2009 (excludes California)

Pros & Cons

👍 Pros

Precise #42 sizing ensures accurate fuel delivery at idle and low throttle, directly improving low-end response on the CRF150R.
High-quality aftermarket construction machined for Keihin carburetor compatibility — threads and seat geometry match OEM specs for a leak-free fit.
Specific application for 2007–2009 Honda CRF150R eliminates cross-compatibility guesswork when ordering.
Small, inexpensive component that can meaningfully restore or improve carburetor performance on a worn or incorrectly jetted bike.
Straightforward installation with a flat-blade screwdriver — no specialty tools needed beyond basic carb service equipment.

👎 Cons

Fitment is limited to 2007–2009 Honda CRF150R — not compatible with other CRF variants, years, or carburetor types without verification.
Cannot be sold to California residents, limiting availability for a significant portion of the U.S. market.
No installation instructions or jetting guidance included — riders unfamiliar with carburetor tuning will need to reference a service manual.
A single pilot jet replacement may not solve jetting issues if the main jet, needle position, or air screw also need adjustment.

Frequently Asked Questions

Which bikes does the Pro X N424-21 #42 pilot jet fit?

This jet is specifically designed for Honda CRF150R models from 2007 through 2009 equipped with Keihin carburetors. California models are excluded due to emissions regulations. Confirm your year and carburetor type before ordering.

What does a pilot jet do, and when do I need to replace or rejet it?

The pilot jet controls fuel delivery at idle and low throttle openings. You'd replace or rejet it if the bike runs lean or rich at idle, has poor low-end throttle response, or if you're adjusting for altitude, temperature changes, or an exhaust/intake modification that shifts the fuel requirement.

Is the #42 size the stock jet for the CRF150R, or is this a rejet?

The #42 designation is the pilot jet size — whether this is stock or a rejet depends on your specific bike's factory jetting. Check the factory service manual for your year CRF150R to confirm OEM pilot jet sizing before installing.

How difficult is it to swap the pilot jet on a CRF150R?

Pilot jet replacement on a Keihin carburetor requires removing the carb from the bike, draining the float bowl, and unscrewing the pilot jet with a flat-blade screwdriver. It's a straightforward job for anyone comfortable removing a carburetor — plan for 30–60 minutes including reassembly and rejetting adjustments.

Why can't this be sold in California?

California Air Resources Board (CARB) regulations restrict the sale of certain aftermarket fuel system components, including carburetor jets, that may affect emissions compliance. This applies regardless of whether the product is OEM-spec or performance-oriented.