The Ultimate Smoothbore Performance: Mikuni HSR42 Easy Kit for Harley Evo

For riders of 1990–1999 Harley-Davidson Big Twin Evolution models, the stock CV carburetor is often the “bottleneck” that prevents the 80-cubic-inch engine from truly breathing. The Mikuni HSR42 Easy Carburetor Kit is widely regarded as the finest performance upgrade available for the Evo platform. Unlike traditional butterfly-style carburetors, the HSR42 features a smoothbore design with a flat slide that moves on roller bearings. This eliminates the turbulence found in stock carburetors, allowing for a straight, high-velocity shot of air and fuel directly into the intake tract. The result is a motorcycle that feels completely transformed, offering instant acceleration and a level of refinement that factory equipment simply cannot match.

The “Easy Kit” Advantage: Performance Without the Hassle

Mikuni designed the “Easy Kit” specifically for the rider who wants maximum performance with a straightforward installation. This kit (often referenced as part number 42-18) is engineered to be a “bolt-on” solution for 1990–1999 Big Twins. What makes it “Easy” is its clever compatibility: it is designed to fit onto your original factory intake manifold and utilizes your stock Harley-Davidson throttle cables. Furthermore, the kit is designed to work with your factory air cleaner cover, allowing you to maintain a sleeper look while hiding a high-performance racing carburetor underneath. This eliminates the need to purchase expensive additional manifolds or cable sets, making it one of the most cost-effective horsepower-per-dollar upgrades on the market.

Precision Engineering and Superior Throttle Response

The standout feature of the Mikuni HSR42 is the roller-bearing throttle slide. While other performance carburetors can feel heavy or “sticky” under vacuum, the Mikuni slide glides effortlessly. This gives the rider a light, precise feel at the grip and provides an instantaneous connection between the throttle and the rear wheel.

• Adjustable Accelerator Pump: The HSR42 features a fully adjustable accelerator pump that allows you to dial in the perfect “squirt” of fuel, eliminating off-idle hesitation and flat spots.
• Advanced Fuel Metering: With a highly sensitive needle and jet system, the Mikuni provides superior atomization, which often leads to improved fuel economy and smoother idling compared to older performance carburetors.
• High-Flow Design: The 42mm bore is perfectly sized for 80″ to 95″ engines, providing enough air for high-lift cams and headwork without sacrificing low-end torque.

Technical Fitment and Installation Notes

This kit is specifically tailored for the 1990–1999 Evolution Big Twin production run.

• Fitment: Fits Softail, Dyna, and Touring models equipped with the 1340cc Evolution engine.
• Standard Components: The kit includes the HSR 42mm carburetor, a specialized air cleaner backing plate adapter, and all necessary mounting hardware.
• Customization: Because the HSR42 is so popular, a wide array of jets and needles are available for riders at high altitudes or those with highly modified engines.
• Reliability: Built with high-quality gaskets and metal components designed to withstand the heat and vibration of an air-cooled V-twin.

Why Choose Mikuni for Your Evolution?

Choosing the Mikuni HSR42 Easy Kit means choosing the “Rider’s Carburetor.” It is a piece of precision Japanese engineering designed to wake up the American soul of your Harley Evolution. You will experience easier starting, a more stable idle, and a ferocious pull through the mid-range that will make your Evo feel like a brand-new machine. Backed by decades of racing heritage, the HSR42 is the standard by which all other Harley carburetors are measured. Don’t settle for the restricted feel of a vacuum-operated carb. Step up to the smoothbore power of Mikuni and feel the difference on every twist of the throttle.

Note: It is recommended to check your spark plug color after the first 50 miles to ensure your jetting is optimal for your specific exhaust and air filter setup.