How to measure a carburetor size?

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While measuring the size of a carburetor, you will notice that multiple misinterpretations are running in people's minds.

Determining the size of a carburetor is actually pretty much easier if you know how you should be doing it.

No matter whether you are thinking about measuring your smaller motorbikes carburetor or larger automotive carburetor, the process is kind of the same for all types.

If you are thinking about measuring the size of the carburetor for the right engine size, this article is here to interpret the procedures in detail so that you can do the job with ease.

Without any further I do, let us jump into the process-

measure carburetor size

The confusion you will face while measuring a carburetor

If you take a carburetor in your hand, you will notice that there are two different holes that go in two different directions.

One of the holes will go to the outlet or to the air filter part, and the other hole will go to the engine compartment. 

While measuring the size of the carburetor, people tend to start measuring at the outlet. But that is not the right way to do it.

You have to start measuring the carburetor at the venturi side that goes to the engine compartment.

Measuring the size of the carburetor

The bore of a carburetor can be both elongated and oval. The size of the bore is what we need to measure to identify the size of a carburetor. Here go the processes you will need to follow-


  1. Telescopic gauge
  2. Slide calipers


  1. When you have a telescopic gauge, measuring the bore becomes much easier.
  2. Put the thin end of the telescopic gauge inside of the carburetor hole and measure the arc.
  3. Release the telescopic gauge, and measure the length with the slide caliper or Varnier caliper. 
  4. The size that you will get will dictate the size of the bore of the carburetor.

An alternative way to measure the size of a carburetor

If you do not have a Telescopic gauge, you can also do the measurement by using a piece of cardboard.

For example, if you have purchased a 19mm carburetor, cut the cardboard with the size of 19mm.

And then try putting the card inside of the carburetor.If the board fits properly to the carburetor, then you are having the right sized carburetor.

If the board does not fit the diameter of the carburetor, the bore of the carburetor must be 1 millimeter off (larger or smaller) than the specific size.

Remember that the inside diameter of the carburetor should match the stated size, not the outer part. 

Carburetor size calculator

There is a simple formula you can use to measure the right size of a carburetor you should use to get the maximum performance from the engine.  The formula is-

Carburetor size = engine size × max rpm × Volumetric efficiency ÷ 3456

The first measurement you will require to measure the right size of a carburetor is the engine displacement size. Every motorcycle or automotive engine comes with a specific engine displacement size.

The next essential aspect you will need to have to measure the right size of a carburetor is the top speed of your vehicle in revolutions per minute or rpm.

The final measurement you will need is the volumetric efficiency of the engine. The Volumetric efficiency of an engine can be anywhere between 70% to 110%. 

Once you have all the specific information in your repertoire, place them on the specific formula to measure the right-sized carburetor you need.

Related post: 
Holley vs. Edelbrock carbureto

A bigger carburetor is not all the time the ideal solution

Many people think that installing a bigger carburetor will allow them to gain more performance. But that is not the reality all the time. You need to choose the size of the carburetor according to the engine size.

Installing a larger carburetor to the engine without being considerate about the engine size may not even allow you to start the engine.

Therefore, be very careful before choosing a larger carburetor to gain the overall performance of your vehicle. If you need to cleaner to remove varnish from carburetor, see our another post.

What are the types of a carburetor?

When it comes to categorizing the types of carburetors, it is possible to categorize carburetors into more than ten different types. But to generalize the category, we have come up with three different types that should include every type of carburetors. Here are the three types of carburetors you would notice while choosing one-

  1. Up-draft carburetor
  2. Horizontal carburetor
  3. Down-draft carburetor

Final summary

  • Measuring the size of a carburetor will not take more than two minutes if you have the right tools. 
  • Automotive carburetors tend to be larger compared to motorcycle carburetors.
  •  Only installing a larger carburetor to your vehicle will not improve the overall performance. You will have to choose the right-sized carburetor that fits perfectly to the outlet of the engine compartment.

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