Modification of the Dell'ORTO PHBG 21 mm four-stroke carburetor version R258 to improve the performance of four-stroke motorcycles and microcars.

This product is the R258 version of the classic Italian 21mm DELL'ORTO PHBG carburetor, specifically optimized for four-stroke engines. It's not simply a replacement for a two-stroke model; its internal metering jet, needle valve, and ports have been specifically adapted to the intake pulsations and combustion characteristics of four-stroke engines. This product offers a ready-to-use, high-quality modification solution for minibikes, street motorcycles, or modified 50-125cc four-stroke engines, significantly improving throttle response and low- and mid-range power. Key benefits include the four-stroke-specific tuning (R258 core): the internal fuel metering system (main jet, idle jet, needle valve profile) has been recalibrated for four-stroke engines, optimizing fuel delivery at low RPMs and part-throttle for more linear torque and immediate throttle response—unlike two-stroke engines, which are designed for rapid acceleration. Ideal bore for small engines: A 21mm bore optimizes the performance of 50-125cc four-stroke single-cylinder engines. It optimally increases intake flow without significantly affecting low-end torque, thus improving mid-range and top-end power. Complete, ready-to-use kit: Typically equipped with vehicle-specific adapters (intake manifold, throttle cable, etc.), it guarantees direct installation without modifications to the frame or the original intake system. Adjustable upgrade platform: While retaining the basic settings of the PHBG series (adjustable mixture screw and needle on some models), this system allows for fine-tuning through modifications to the air filter and exhaust. Improved performance and riding enjoyment: After the upgrade, the most noticeable improvements are better throttle response, smoother power delivery, and more responsive mid-range acceleration, significantly enhancing the riding experience of small vehicles. Compatibility Information: Target Engine: Single-cylinder, four-stroke (4T) gasoline engine. Compatible Displacement Sizes: 50cc, 70cc, 90cc, 110cc, 125cc, and other common small-displacement models. Compatible Models: Honda MSX125 (GROM) and similar minibikes (engine compatibility must be verified). Various minibikes and light street motorcycles. Small off-road motorcycles and superbikes (4-stroke models). Conversion projects for certain small universal 4-stroke engines. Important Note: "R258" is the designation of a modified version and not a standard Dell Otto model. Please check before purchasing whether this version has been successfully used on your vehicle and whether the included adapter kit is fully compatible with your engine's intake manifold. The kit includes a modified PHBG 21mm R258 carburetor body.