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Start ShoppingMIKUNI F4/042-390 Hex Main Jets - Precision Brass Fuel Jets for High-Performance Engines
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Description
Upgrade your engine's fuel delivery system with MIKUNI's F4/042-390 hex main jets. These precision-engineered brass jets deliver consistent fuel metering for enhanced power, efficiency, and reliability in high-performance engines.
Key Features
- Brass Construction: Durable, corrosion-resistant material ensures long-lasting performance in demanding environments.
- 0.130" Orifice Size: Precisely calibrated for optimal fuel flow rates, matching MIKUNI carburetor specifications.
- M5 x 0.75 Thread Size: Universal compatibility with standard carburetor setups for easy installation.
- Hex Head Design: Simplifies adjustment and maintenance while reducing the risk of cross-threading.
Why Choose This Product
These jets are engineered for riders who demand precision and reliability. The brass material resists clogging and wear, while the calibrated orifice size ensures perfect fuel-air mixture for maximum horsepower. Ideal for racing, off-road, and high-performance motorcycles, these jets deliver consistent performance under extreme conditions. Their lightweight design (0.5 oz) minimizes engine load without compromising durability.
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Upgrade your engine's fuel delivery system with MIKUNI's F4/042-390 hex main jets. These precision-engineered brass jets deliver consistent fuel metering for enhanced power, efficiency, and reliability in high-performance engines.
Key Features
- Brass Construction: Durable, corrosion-resistant material ensures long-lasting performance in demanding environments.
- 0.130" Orifice Size: Precisely calibrated for optimal fuel flow rates, matching MIKUNI carburetor specifications.
- M5 x 0.75 Thread Size: Universal compatibility with standard carburetor setups for easy installation.
- Hex Head Design: Simplifies adjustment and maintenance while reducing the risk of cross-threading.
Why Choose This Product
These jets are engineered for riders who demand precision and reliability. The brass material resists clogging and wear, while the calibrated orifice size ensures perfect fuel-air mixture for maximum horsepower. Ideal for racing, off-road, and high-performance motorcycles, these jets deliver consistent performance under extreme conditions. Their lightweight design (0.5 oz) minimizes engine load without compromising durability.
| SKU | GMBDA37F55 |
|---|---|
| MPN | F4/042-390 |
| Brand | MIKUNI |
| Category | Jets |
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Featured Review
| Make | Model | Years |
|---|---|---|
| Various Japanese | Multiple carbureted models (Keihin/Mikuni carbs) | 1985-2024 |
| Suzuki | RM/DR-Z series | 1990-2010 |
Frequently Asked Questions
This is a #390 main jet (large size for high-altitude or rich jetting needs).
Yes, compatible with most Mikuni round/flat slide carbs and many Keihin replacements.
Often yes, pair with pilot jet and needle for complete tuning.
Genuine Mikuni OEM quality part.
Installation Guide
Difficulty
Easy
Est. Time
5 min
Tools Required
- Small flathead screwdriver
- Jet cleaning wire or compressed air
Pro Tips
- Remove float bowl, unscrew old jet with screwdriver, note size, install new one hand-tight plus quarter turn
Common Mistakes to Avoid
- Not cleaning carb passages before install
- Incorrect jet size selection
Comparison vs Stock/OEM
Direct OEM replacement or upgrade; identical to factory Mikuni jets
Improvements
- Precise machining for consistent fuel flow
- Corrosion-resistant brass
Considerations
- Must select correct size based on mods/exhaust/air filter
Durability & Warranty
Expected Lifespan
Indefinite with proper cleaning; replace when worn or clogged
Warranty
Manufacturer defect warranty (typically 1 year)
Maintenance
Clean with jet cleaner every 10-20 hours; inspect during carb service
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