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Start ShoppingMIKUNI F4/042-320 Hex Main Jets - Brass Fuel Jets for Precision Fuel Metering
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Description
Upgrade your engine's fuel delivery system with MIKUNI's F4/042-320 Hex Main Jets. These precision-engineered brass jets ensure optimal fuel-air mixture for enhanced power, efficiency, and engine longevity in motorcycles and off-road vehicles.
Key Features
- Material: Durable brass construction for corrosion resistance and long-term reliability
- Jet Size: #320 diameter for precise fuel metering in main circuit applications
- Thread Type: Hex head design for secure, vibration-resistant installation
- Flow Rate: Engineered for consistent fuel delivery across varying RPM ranges
- Dimensions: Standard Mikuni main jet size (approx. 6mm diameter) for universal compatibility
Why Choose This Product
These main jets deliver unmatched performance through precise fuel metering, ensuring your engine runs smoothly under all conditions. The brass material resists corrosion and maintains accuracy over time, while the hex head thread provides a secure fit to prevent fuel leaks. Perfect for tuning high-performance engines, these jets offer reliable fuel delivery without compromising power or efficiency.
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Upgrade your engine's fuel delivery system with MIKUNI's F4/042-320 Hex Main Jets. These precision-engineered brass jets ensure optimal fuel-air mixture for enhanced power, efficiency, and engine longevity in motorcycles and off-road vehicles.
Key Features
- Material: Durable brass construction for corrosion resistance and long-term reliability
- Jet Size: #320 diameter for precise fuel metering in main circuit applications
- Thread Type: Hex head design for secure, vibration-resistant installation
- Flow Rate: Engineered for consistent fuel delivery across varying RPM ranges
- Dimensions: Standard Mikuni main jet size (approx. 6mm diameter) for universal compatibility
Why Choose This Product
These main jets deliver unmatched performance through precise fuel metering, ensuring your engine runs smoothly under all conditions. The brass material resists corrosion and maintains accuracy over time, while the hex head thread provides a secure fit to prevent fuel leaks. Perfect for tuning high-performance engines, these jets offer reliable fuel delivery without compromising power or efficiency.| SKU | GMB271A648 |
|---|---|
| MPN | F4/042-320 |
| Brand | MIKUNI |
| Category | Jets |
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Featured Review
| Make | Model | Years |
|---|---|---|
| Various | Mikuni TM/VM series carbureted motorcycles/ATVs | 1980-2025 |
| Yamaha | XT600, YZ250F, WR250 | 1990-2010 |
| Suzuki | DR350, DRZ400 | 1985-2005 |
| Kawasaki | KLX300, KX500 | 1995-2015 |
Frequently Asked Questions
Fits Mikuni TM, VM, and BS series carbs with main jet position (most 2-stroke and 4-stroke bikes/ATVs). Confirm your carb model.
Use plug chop method: ride WOT, kill engine, check spark plug color. Lean = larger jet (#320 is for richer mixtures).
Yes, OEM Mikuni part F4/042-320, not aftermarket copy.
Yes, ideal for rejetting after airbox mods, exhaust, or elevation changes above 3000ft.
Installation Guide
Difficulty
Easy
Est. Time
5 min
Tools Required
- Small flathead screwdriver
- Jet cleaning needle or wire
Pro Tips
- Remove carb, unscrew old jet with screwdriver, note position, install new jet finger-tight then snug. Always re-jet in pairs (pilot + main) and test plug chop for tuning
Common Mistakes to Avoid
- Not cleaning carb passages before install
- Installing wrong size jet
Comparison vs Stock/OEM
Direct OEM replacement or upgrade for worn jets/stock jetting
Improvements
- Precise fuel delivery for optimal A/F ratio
- Better throttle response and power
- Corrects lean/rich conditions from mods
Considerations
- Requires tuning knowledge; not plug-and-play without testing
Durability & Warranty
Expected Lifespan
Indefinite with proper cleaning (replace if clogged or damaged)
Warranty
Mikuni lifetime against defects
Maintenance
Clean with carb cleaner every 10-20 hours; inspect during service
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