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Start ShoppingMIKUNI F4/042-640 Hex Main Jets - High-Performance Brass Carburetor Jets for Racing & Off-Road
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Description
Upgrade your carburetor's fuel delivery system with MIKUNI's F4/042-640 Hex Main Jets. These precision-engineered brass jets deliver consistent performance and reliable fuel-air mixture control for racing, off-road, and high-output motorcycle applications.
Key Features
- Brass Construction: Durable, corrosion-resistant material ensures long-lasting performance in demanding environments.
- #640 Jet Size: Optimized flow rate for precise fuel metering in high-performance engines.
- Hex Head Design: Easy installation and adjustment with 4mm orifice for accurate fuel delivery.
- M5 x 0.75 Thread: Standard thread size ensures compatibility with most carburetor systems.
Why Choose This Product
MIKUNI's Hex Main Jets offer unmatched reliability and precision for riders seeking peak engine performance. The brass material resists wear and corrosion, while the hex head design simplifies maintenance. Whether you're tuning a racing bike or enhancing an off-road machine, these jets provide consistent fuel flow for improved power, throttle response, and engine efficiency. Perfect for mechanics and riders who demand precision in every ride.
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Upgrade your carburetor's fuel delivery system with MIKUNI's F4/042-640 Hex Main Jets. These precision-engineered brass jets deliver consistent performance and reliable fuel-air mixture control for racing, off-road, and high-output motorcycle applications.
Key Features
- Brass Construction: Durable, corrosion-resistant material ensures long-lasting performance in demanding environments.
- #640 Jet Size: Optimized flow rate for precise fuel metering in high-performance engines.
- Hex Head Design: Easy installation and adjustment with 4mm orifice for accurate fuel delivery.
- M5 x 0.75 Thread: Standard thread size ensures compatibility with most carburetor systems.
Why Choose This Product
MIKUNI's Hex Main Jets offer unmatched reliability and precision for riders seeking peak engine performance. The brass material resists wear and corrosion, while the hex head design simplifies maintenance. Whether you're tuning a racing bike or enhancing an off-road machine, these jets provide consistent fuel flow for improved power, throttle response, and engine efficiency. Perfect for mechanics and riders who demand precision in every ride.
| SKU | GM7EB95AC5 |
|---|---|
| MPN | F4/042-640 |
| Brand | MIKUNI |
| Category | Jets |
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Featured Review
| Make | Model | Years |
|---|---|---|
| Various | Mikuni TM/VM/PF series carburetors | 1980-2025 |
| Yamaha | XT600, YZ series | 1990-2010 |
| Honda | CRF, XR series | 1985-2020 |
Frequently Asked Questions
Fits Mikuni TM, VM, PJ, and PF series carbs with hex main jet holder; check your carb model.
Jet size depends on altitude, mods, and fuel; start with OEM size and adjust based on plug reads.
Hex jets have wrench flats for easier removal without special tools.
Usually not directly; some adapters exist but confirm thread match.
Installation Guide
Difficulty
Easy
Est. Time
5 min
Tools Required
- Small flathead screwdriver
- Jet needle tool or pick
Pro Tips
- Remove float bowl completely for access; note original jet size before swapping
Common Mistakes to Avoid
- Not cleaning carb passages before install
- Incorrect jet size selection
Comparison vs Stock/OEM
Direct OEM replacement or upgrade for worn jets; same brass material
Improvements
- Precise fuel metering for better performance tuning
- Easier install with hex head
Considerations
- Precision machined; avoid cheap knockoffs
Durability & Warranty
Expected Lifespan
Indefinite with proper maintenance; resistant to fuel corrosion
Warranty
Limited lifetime from Mikuni
Maintenance
Inspect during carb cleans; replace if clogged or damaged
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