Find your Holley carburetor model number on the casting itself

The model number is stamped or cast into the body of the carburetor, usually on the passenger side of the main body or on the air horn (the top piece). Look for a series of numbers, often four to six digits, sometimes followed by letters. This number is your primary identifier and will tell you the carburetor's size, fuel delivery system, and intended process.

If the casting is dirty or corroded, clean the area with a wire brush or fine steel wool to make the numbers readable. Take a photo with your phone if the stamping is shallow — the image often shows detail better than your eye can see in person. Write down the complete number exactly as it appears, including any letters or dashes.

The location varies slightly by era and model family. On older two-barrel carburetors, the number may be on the base of the carburetor where it bolts to the manifold. On four-barrel models, check both the driver and passenger sides of the main body before assuming the number is missing.

Key Takeaways

  • The model number is stamped into the carburetor casting and is your primary tool for identification — write it down exactly as it appears, including any letters.
  • Holley carburetors are sorted by barrel count (two, four, or six barrels), fuel delivery method (vacuum secondary or mechanical secondary), and process (street, racing, marine).
  • The first digits of the model number usually indicate barrel count and fuel system type, while later digits specify the exact configuration and year range.
  • If you cannot find a casting number, measure the carburetor's overall dimensions and the diameter of the intake mounting flange to narrow down the model family.
  • Online Holley identification databases and carburetor rebuild kits cross-reference model numbers to specifications, so you can confirm your number before ordering parts.

Understand what the model number tells you

Holley model numbers follow a pattern that reveals the carburetor's core characteristics. The first two or three digits typically indicate the barrel count and fuel delivery system. A number starting with 2 usually means a two-barrel carburetor. Numbers starting with 4 indicate a four-barrel. Numbers in the 6000 range are six-barrel models, though these are less common in street applications.

The next digits specify whether the carburetor uses a vacuum secondary (the secondary barrels open gradually as engine vacuum increases) or a mechanical secondary (the secondary barrels open in direct proportion to throttle position). Vacuum secondary models are common on street engines because they deliver fuel more smoothly. Mechanical secondary models are preferred for racing because they open fully and when ready when you press the throttle.

The final digits and any letters indicate the specific configuration — which jets are installed, what float level is set, whether it has an electric choke, and what year or process it was designed for. Two carburetors with the same first four digits but different final digits may look identical but have different internal calibrations.

Recognize common Holley carburetor families by appearance

Two-barrel Holley carburetors are compact and sit on a single mounting flange. They have one fuel inlet and typically one choke mechanism. These are common on four-cylinder engines and smaller V-8s. The casting is usually narrower than a four-barrel and the air horn is proportionally smaller.

Four-barrel Holley carburetors have a larger, more rectangular body with two fuel inlets (one for the primary barrels, one for the secondary). The air horn is taller and wider. Most street and performance four-barrels have a vacuum secondary diaphragm mounted on the driver side of the main body — it looks like a small cylindrical can bolted to the side. Mechanical secondary models have a linkage rod connecting the throttle shaft to the secondary throttle plates instead.

Six-barrel models are visibly wider and taller than four-barrels and are rarely seen outside of marine or specialized racing applications. If you are looking at a carburetor on a street car or truck, it is almost certainly a two or four-barrel.

Measure the carburetor if the casting number is worn or missing

If the model number is completely illegible, measure the diameter of the intake mounting flange (the circular or oval opening where the carburetor bolts to the engine). Two-barrel carburetors typically have a flange diameter of 1.5 inches. Four-barrel flanges are usually 2.0 to 2.25 inches. This measurement alone narrows the field significantly.

Next, measure the overall width and height of the main body (not including the air horn). Write these down in inches. Then count the visible fuel inlet ports on the side of the carburetor — two-barrels have one, four-barrels have two. Check whether the carburetor has a vacuum secondary diaphragm (a cylindrical can on the side) or mechanical linkage rods.

Take a clear photo of the entire carburetor from the side and front, showing the air horn, main body, and any visible linkage or diaphragm. Post the photo and your measurements on a carburetor identification forum or send them to a Holley distributor — they can often identify the model family from appearance and dimensions alone, even without a casting number.

Cross-reference your model number in Holley's documentation

Holley publishes identification guides and specification sheets for most models produced since the 1960s. The easiest source is the Holley website's technical library, which includes PDF documents organized by model family. Search for your model number in the document title or use the site's search function.

Carburetor rebuild kit boxes also include identification charts. If you are planning to rebuild the carburetor, order a kit for your model number — the kit box will list the model number, process, and year range, confirming you have the right part. Do not open the kit until you have verified the number matches.

Online carburetor forums and enthusiast sites maintain searchable databases of Holley models. Post your model number and a photo, and experienced users will usually confirm the model, process, and any known quirks or common issues within a few hours. These communities are particularly useful if your carburetor is an older or unusual variant.

Distinguish between original and replacement carburetors

A carburetor stamped with a model number was either original equipment from the manufacturer or a direct replacement sold by Holley. Original equipment carburetors are calibrated for a specific engine, year, and emissions standard. A replacement carburetor sold as an aftermarket part may have a different model number even though it fits the same engine.

If you are restoring a vehicle and need to know what carburetor came on it originally, look up the engine code and year in the vehicle's service manual. The manual will list the original carburetor model. If you are working on a vehicle that has already been modified, the carburetor you find may be a later upgrade or a different process entirely.

Holley also produced carburetors under other brand names, including Autolite and Carter. If your carburetor is stamped with one of those names, it may still be a Holley design, but the model numbering system will be different. Check the brand name on the casting before searching for documentation.

Verify the carburetor's fuel system type before ordering parts

Once you have identified the model number, confirm whether the carburetor uses a vacuum secondary or mechanical secondary before ordering a rebuild kit or replacement parts. A vacuum secondary kit will not fit a mechanical secondary carburetor, and vice versa. The difference is visible from the outside — look for a diaphragm can on the side (vacuum) or linkage rods (mechanical).

Also note whether the carburetor has an electric choke (a small solenoid mounted on the choke housing) or a manual choke. Electric choke carburetors require a 12-volt power source and will not work correctly if the power connection is missing or corroded. Manual choke carburetors have a cable or rod that you operate by hand.

The model number itself usually encodes this information, but visually confirming it prevents ordering the wrong kit. When you order a rebuild kit or replacement gasket set, provide both the model number and a photo showing the secondary type and choke style. The supplier can then confirm they are sending the correct parts for your specific carburetor.

Frequently Asked Questions

What if the model number has letters after the digits?

Letters at the end of the model number indicate a specific variant or revision. For example, a model number ending in "A" or "B" means the carburetor was updated or recalibrated after the original release. These variants usually have the same basic structure but may have different jets or float settings. Include the letters when you search for documentation or order parts.

Can I use a Holley carburetor from a different process on my engine?

Physically, yes — if the mounting flange matches, the carburetor will bolt on. But the fuel delivery will not be optimized for your engine. A carburetor calibrated for a different displacement, fuel type, or emissions standard may run too rich or too lean. For reliable performance, use a carburetor designed for your specific engine or have it professionally rejetted by someone familiar with Holley tuning.

Where is the model number on a Holley four-barrel?

On most four-barrel models, the casting number is on the passenger side of the main body, usually near the secondary fuel inlet. On some older models, it is stamped on the base where the carburetor bolts to the manifold. If you cannot find it on the main body, flip the carburetor upside down and check the underside of the base plate.

What does "2300" or "4150" mean in a Holley model number?

These are family designations that Holley has used for decades. The 2300 is a two-barrel carburetor family. The 4150 is a four-barrel family. Carburetors within the same family share the same basic structure and mounting, but different model numbers within that family indicate different calibrations or secondary types. Knowing the family helps you find the right rebuild kit and understand which parts are interchangeable.

How do I know if my carburetor is original to the vehicle?

Check the vehicle's service manual or owner's manual for the original carburetor specification. Compare that model number to the one on your carburetor. If they match, the carburetor is likely original (or a direct factory replacement). If the numbers are different, the carburetor has been swapped at some point. This does not mean it is wrong — it just means the vehicle has been modified.