Mikuni 003.157 VM40/02 Aluminum Throttle Valve Slide - Left-Hand - Cutaway 2.5

The Mikuni 003.157 is a genuine OEM-spec replacement throttle valve (slide) designed for the Mikuni VM40/02 round slide carburetor. Constructed from lightweight aluminum, this slide is a direct-fit replacement for worn or tuning-specific applications on VM Series carburetors using 40mm and 44mm spigot configurations.

The cutaway number of 2.5 refers to the size of the angled notch cut into the bottom of the slide. This cutaway directly influences fuel mixture from approximately 1/8 to 1/2 throttle — a smaller number yields a richer mixture, while a larger number produces a leaner mixture. The 2.5 cutaway represents a mid-range tune suitable for a wide variety of engine setups.

This valve features a Left-Hand (LH) idle screw position. To identify handedness, view the slide from the intake side with the cutaway facing you — if the idle adjustment screw is on the left side, it is a left-hand valve.

Key Specifications:

• OEM Part Number: 003.157 (also referenced as 003-157)
• Cutaway Size: 2.5 (VM40/02 specification)
• Material: Aluminum
• Idle Screw Position: Left-Hand (LH)
• Compatible Spigot Sizes: 40mm and 44mm
• Fits: Mikuni VM Series round slide carburetors

The Mikuni VM Series round slide carburetor is among the most widely used high-performance single carburetors in powersports, proven across motocross, enduro, trail riding, flat track, and road racing on both 2-stroke and 4-stroke engines. Replacing the throttle valve with the correct cutaway size is one of the most effective ways to fine-tune mid-range fuel delivery for your specific engine and application.