What size is my motorcycle carburetor?

Measure the opening of the body on the intake manifold side in mm. That will equal the model number like Mikuni VM26 = 26mm bore.

How do I know what CFM my carburetor is?

The formula for calculating how much CFM (cubic feet per minute) your engine requires is: CFM = Cubic Inches x RPM x Volumetric Efficiency ÷ 3456.

How do I know my main jet size?

Consult your manual first to find the stock size. Also pay attention to the numbers on the side of your old jets, which you’ll be able to see in the steps to come. A larger jet number means a bigger hole and more fuel. A smaller jet number has smaller holes and should be used if your engine needs to run more lean.

How do I know what size carb jet I have?

For example, a jet may be stamped (on its head) with the number 30. This indicates that the jet’s size is 30 mm. Installing a smaller size jet will reduce fuel flow, which is ideal for high-altitude conditions where air is limited, where a larger jet size increases fuel flow for oxygen-rich, low altitudes.

Are all carb jets the same?

Nearly all MX bikes use the same carb, the FCR. Almost all the jets are the same.

What does mm mean in carburetor?

Measure the venturi (in mm), which is the smallest diameter inside the bore of the carb.

How do I know what size of carburetor I have?

Examine the engine end of the carburetor and you may find the stamped marking like HSR 42 or similar to that which indicates the design and size of your carburetor.

What size carburetor do I need for my race engine?

TMX series carburetors of 35 mm bore size are used for 125 cc race engines whereas 38 mm bore size is used for 250 cc race engines. (This information is compiled from the Mikuni Catalog.

Why check the carburetor on a motorcycle first?

Carburetor malfunctions can be pretty frustrating. In my experience, when a motorcycle starts acting up I check the carburetor first because that’s usually the culprit. Sometimes it can be difficult to know whether or not it’s the carburetor causing the problem.

What is the bore size of a Mikuni carburetor?

If the bore size is 48 mm, your carburetor number is HSR 48 since there is only one Mikuni carburetor with a 48 mm bore size (Table-1). Similarly, if the bore size is 42 mm, you have Mikuni HSR 42 whereas a bore size of 45 mm indicates an HSR 45.