Carburetor Metering Block Conversion Kit

What Is a Carburetor Metering Block Conversion Kit?

A carburetor metering block conversion kit allows you to replace the fixed secondary metering plate on many popular carburetors with a fully adjustable billet metering block. On carburetors like the Holley 4160 series, the secondary side often comes from the factory equipped with a simple metering plate — a non-adjustable component that meters fuel through fixed restrictions. While this setup works fine for a stock engine, it becomes a significant limitation the moment you start modifying your motor.

Proform Parts offers billet secondary metering block conversion kits designed to unlock the tuning potential of your carburetor without requiring a full carb replacement.

Metering Plate vs. Metering Block: Why It Matters

The difference between a metering plate and a metering block comes down to tunability. A metering plate is a thin, stamped piece with fixed orifices — what you see is what you get. A metering block, by contrast, accepts changeable main jets, allowing you to dial in the secondary fuel curve to match your engine's actual demands. Carburetor metering block conversion kits bridge that gap, letting enthusiasts convert a budget-friendly vacuum-secondary carburetor into a fully tunable performance piece.

This matters especially once you've made engine modifications — a cam upgrade, cylinder head work, intake manifold swap, or forced induction all change the air/fuel requirements of your engine. With a fixed metering plate, you're stuck with whatever calibration the factory chose. With a metering block, you can swap jets, adjust idle feed restrictions, and fine-tune the fuel curve to suit your specific combination.

What's Typically Included in a Conversion Kit

A quality metering block conversion kit packages everything needed for the swap in one box. Most kits include:

• A billet aluminum secondary metering block (often black or natural anodized)
• A longer transfer tube to accommodate the increased thickness of the block versus the plate
• Longer fuel bowl screws
• All necessary gaskets and seals for a leak-free installation

Some kits — particularly those designed for double-pumper or dual-inlet carburetors — also include provisions for a four-corner idle system, which routes idle circuit fuel to all four corners of the throttle bore for improved idle quality and off-idle response. Always verify that your throttle body is compatible with this feature before selecting your kit.

Fitment Considerations

Not all conversion kits are interchangeable. The two primary variables are carburetor model and fuel inlet style. Single-inlet and dual-inlet carburetors require different kits due to differences in the fuel delivery plumbing. Similarly, vacuum secondary carburetors (like the Holley 4160) and mechanical secondary "double pumper" carburetors (like the Holley 4150) have different secondary circuit configurations. Always cross-reference your carburetor's model number before purchasing a conversion kit.

Proform Parts Metering Block Conversion Kits

Proform Parts is a well-regarded name in carburetor components and engine dress-up, producing metering block conversion kits for a range of Holley-style carburetors. Their billet aluminum blocks feature a black anodized finish and are engineered to fit both single-inlet and dual-inlet vacuum secondary applications, as well as double-pumper 4150-style carburetors. Proform kits include all necessary gaskets and hardware, making them a straightforward bolt-in upgrade for the performance-minded builder.