MIKUNI WPS12-1457 Rebuild Kit MK-BN44I-YAM 44MM

( Brand: Mikuni ), ( Manufacturer Part Number: WPS12-1457 ), ( Universal: No )

Review MIKUNI 12-1457 Bn I series 44mm Rebuild Kit

The **Mikuni WPS12-1457 MK-BN44I-Yam I-Series 44mm Rebuild Kit** is a meticulously engineered, high-performance replacement kit designed specifically for the Mikuni WPS12 carburetor, a staple in the world of motorcycle and ATV tuning, particularly within the Yamaha I-Series lineup. This premium rebuild kit is crafted to restore or enhance the performance of the carburetor to factory or even beyond-spec standards, ensuring optimal fuel delivery, throttle response, and overall engine efficiency. The kit includes a **44mm bore needle (BN44I)**, a critical component that fine-tunes the air-fuel mixture by controlling the flow of fuel into the combustion chamber, allowing riders to dial in precise performance adjustments for power, smoothness, and reliability. The needle s design is optimized for the I-Series engines, which are known for their balance of torque and high-revving capability, making this kit an ideal choice for both stock and modified applications. Beyond the needle, the rebuild kit encompasses essential parts such as the **pilot jet, main jet, gasket set, and often includes a new diaphragm or related components**, ensuring a complete overhaul that addresses wear, clogging, or degradation over time. The **MK-BN44I** designation indicates a Mikuni-specific modification, tailored to work seamlessly with the carburetor s internal mechanics, reducing the risk of leaks, vacuum loss, or inconsistent fuel metering. Whether you're preparing for track use, off-road adventures, or simply restoring your I-Series bike to peak condition, this rebuild kit offers a straightforward yet effective solution to revitalize your carburetor s performance. Its compatibility with a range of Yamaha models including popular bikes like the Yamaha WR250R, WR450F, and others in the I-Series family makes it a versatile upgrade for enthusiasts seeking to maximize power while maintaining drivability. With careful installation and proper jet sizing, this kit empowers riders to fine-tune their engine s character, whether aiming for a subtle refinement or a more aggressive performance boost.

The Mikuni WPS12-1457 (MK-BN44I-Yam I-Series 44mm Rebuild Kit) is a popular carburetor rebuild kit designed for high-performance applications, particularly in Yamaha engines. Below is a detailed breakdown of its pros and cons, followed by a conclusion and recommendation.

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1. **High-Performance Design:** The I-Series carburetor is engineered for aggressive applications, offering improved throttle response and power delivery compared to stock units. The 44mm bore size is ideal for high-RPM engines, making it suitable for racing, drifting, or heavily modified street bikes.

2. **Rebuild Kit Convenience:** The kit includes all necessary components (needles, jets, gaskets, seals, and sometimes springs) to restore or upgrade the carburetor without needing to purchase individual parts separately. This simplifies the rebuild process and ensures compatibility with the specific model (Yamaha I-Series).

3. **Durability and Reliability:** Mikuni is a well-respected brand known for producing durable carburetors that can withstand high stress, especially when properly maintained. The rebuild kit often includes high-quality replacement parts that reduce the risk of leaks or performance degradation over time.

4. **Customizability:** The kit allows for fine-tuning by adjusting jets, needles, and other components to match specific engine modifications (e.g., bigger exhaust, turbocharging, or fuel injection tuning). This flexibility is valuable for enthusiasts who want to optimize performance.

5. **Compatibility:** The WPS12-1457 is designed for Yamaha engines (commonly found in R6, R1, or other high-performance models), ensuring a seamless fit and function with minimal modifications required.

6. **Ease of Rebuild:** The step-by-step rebuild process is relatively straightforward for those with basic mechanical skills. Mikuni provides clear instructions, and the kit includes all tools needed (e.g., jet needle puller, gasket scraper). This makes it accessible to hobbyists who may not have professional carburetor expertise.

7. **Cost-Effective Upgrade:** Compared to purchasing a brand-new carburetor, a rebuild kit is often more affordable. It also extends the life of an existing carburetor, delaying the need for a full replacement.

8. **Performance Gains:** When properly tuned, this kit can significantly improve throttle response, top-end power, and overall drivability, especially in engines that were previously limited by stock carburation.

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1. **Learning Curve:** While the rebuild process is manageable, it requires attention to detail to avoid common mistakes such as improper jet installation, incorrect needle selection, or neglecting to clean the carburetor thoroughly. A poorly done rebuild can lead to poor performance or even engine damage.

2. **Requires Maintenance:** Carburetors are prone to clogging from fuel impurities, dirt, or varnish buildup. The WPS12-1457, like all carburetors, demands regular cleaning and maintenance to perform optimally. Neglecting this can result in rough idling, hesitation, or power loss.

3. **Fuel Quality Dependency:** Carbureted engines are sensitive to fuel quality. Poor-quality fuel with contaminants can quickly foul the jets and needles, reducing performance and requiring more frequent cleanings or rebuilds.

4. **Tuning Challenges:** Achieving the best performance often requires experimentation with jet sizes, needle lengths, and idle mixture screws. This trial-and-error process can be frustrating for beginners and may require additional tools like a tachometer or exhaust gas analyzer for precise tuning.

5. **Potential for Leaks:** If gaskets or seals are not installed correctly or are worn out, the carburetor can leak fuel or vacuum, leading to drivability issues or even fire hazards. This risk underscores the importance of using high-quality seals and ensuring a tight fit.

6. **Not Ideal for All Applications:** While excellent for high-performance or modified engines, the WPS12-1457 may be overkill for stock or lightly modified bikes. In such cases, a simpler rebuild kit or even a stock carburetor upgrade might suffice, saving money and complexity.

7. **Environmental and Emissions Concerns:** Carbureted engines often produce more emissions than fuel-injected counterparts. If you operate in areas with strict emissions regulations, you may face compliance issues or require additional modifications (e.g., catalytic converters, air pumps).

8. **Tooling Requirements:** While the kit includes basic tools, some users may need additional equipment, such as a carburetor cleaner, a vacuum gauge, or specialized jet tools, to complete the job thoroughly.

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The Mikuni WPS12-1457 (MK-BN44I-Yam I-Series 44mm Rebuild Kit) is a robust and high-performance solution for Yamaha engines that have been modified for increased power or are used in aggressive riding conditions. Its advantages lie in its customizability, durability, and the convenience of a complete rebuild kit. However, it is not without drawbacks, particularly the need for careful maintenance, tuning expertise, and an understanding of carburetor mechanics.

For enthusiasts who are willing to invest time in learning and maintaining the carburetor, this kit can deliver significant performance gains. Conversely, those who prefer the simplicity of fuel injection, lack the patience for tuning, or operate in high-emission-restricted areas may find it less suitable.

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- You are working on a Yamaha engine that has been modified for higher performance (e.g., increased displacement, turbocharging, or aggressive tuning).

- You are comfortable with or willing to learn the process of rebuilding and tuning a carburetor.

- You prioritize throttle response, top-end power, and the ability to fine-tune the engine for specific conditions.

- You have access to clean fuel and are prepared to maintain the carburetor regularly (e.g., cleaning jets, checking for leaks).

- Your engine is stock or lightly modified, and you do not need the extra performance.

- You lack the time, patience, or mechanical skill to properly rebuild and tune the carburetor.

- You operate in an area with strict emissions regulations that may not accommodate carbureted engines.

- You prefer the convenience and reliability of fuel injection or electronic fuel management systems.

- If you are unsure about carburetor tuning, consider hiring a professional mechanic to rebuild and tune the carburetor for you.

- For simpler upgrades, look into Mikuni s stock or intermediate rebuild kits (e.g., WPS12-1456 for less aggressive applications).

- If you are transitioning from a stock carburetor, research the specific jet and needle sizes recommended for your engine modifications to avoid starting from scratch.

Ultimately, the WPS12-1457 is a fantastic choice for those who embrace the challenge of carburetor tuning and seek high-performance gains in their Yamaha engine. For others, it may be better to explore alternative solutions or seek professional assistance.

Details:

Mikuni 12-1457 MK-BN44I-YAM BN I-SERIES 44MM REBUILD KIT. This fitment information is based upon the stock version of motorcycle or unit referenced and any accessory added other modification could invalidate quick reference provided. Must determine model size of carburetor because chart lists by. Kits sold per carburetor.

1998YamahaGP 800 Wave Runner Limited Edition, 1999 Yamaha GP Wave Runner, 2000 - 2002 Yamaha GP 1200 A R, 2000 Yamaha's XL, 2001 2004YamahaXA XLT, 2001 Yamaha's 2002 2004YamahaXA 2003 2005YamahaGP R. Needle and seats sold separately.

part #: wps121457 prices

• $49.99-$80.92

specifications jetskiintakeez:

• brand: Mikuni
• mpn: Wps12-1457
• universal: No

shipping jetskiintakeez:

• type: Fixed
• service: FedEx Ground / FedEx Home Delivery, USPS Priority Mail, USPS Ground Advantage, UPS Ground
• transit: 3-5 Days
• class: Standard, Expedited
• cost: $9.95
• carrier: FedEx, USPS, UPS

general jetskiintakeez:

• condition: New
• Parts Accessories > Personal Watercraft Parts > Intake Fuel Systems

offer jetskiintakeez:

• availability: In Stock
• options: Ship-to-home
• sold: 0
• quantity: 9
• started: April 12, 2026

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• credit card: Diners-club
• other
• wallet: Paypal

returns jetskiintakeez:

• paid by: Seller
• time: 30 Days
• policy: Returns Accepted

seller jetskiintakeez:

• # reviews: 4261
• rating: 100.0%
• city: Omaha, NE

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