I also have the HRC manual in pdf that shows this jet with the correct code somewhere in the float near to the emulsion tube but it is not very specified.
I dont understand if it is for pressing it near the emulsion tube to the power jet tube as Andy said why it is only one including at the kit and the HRC manual as the NSR has two carbs?
The other way,why HRC include this jet for repalce to the Y solenoid if the kit has already the HRC Y and X solenoids inside ready with the correct jets?It doesnt make sense.
I will go tommorow to my Honda dealer to get some orders and i will take a photo from his manual who include also this jet in the diagram somewhere in the float to take a look.
Thanks for the interest