Guide: To find the needle jet you need go click here, choose your carb style, click parts / accessories, then parts to the exploded view drawing. Find the needle jet number style in the chart and click it. Then you will be at your needle jet category.
Function: The needle jet is the main fuel passage to the main bore (venturi) of the carburetor. Depending on the inside diameter of a specific needle jet, this will also effect the function of the needle. therefore, needle jets and jet needles act togeher as the main system in controlling the amount and mixture of the fuel which is drawn in mid-range (1/4 - 3/4) throttle operation.
Needle jets are available not only in types, but by series and size. Mikuni series numbers for style of the needle jet. This series includes not only the physical fitment dimensions but also the nozzle profile, and the atomization pattern. The sizes (inside diameter size) within each series are listed according to a letter-number combination. The letter shows the inside diameter size in increments of .50mm. See the Mikuni Needle Jet Sizing Chart below for a better understanding.