[mike dawson]

just gutted my exhaust and uncorked the air box i installed a 115 main jet the bike runs great and the plug looks good should i put the performance needle and the 42 pilot in or not

[oldtimer]

The power up needle and needle jet had a different shape/profile. Your main jet sits below the needle and meters the bulk flow of fuel above 3/4 throttle. Before 3/4 and above 1/4 the needle shape and how it fits into the needle jet determine how much fuel is delivered at what throttle opening in this range. This needle is intended to deliver more fuel in this range.
The reason behind the uncork is to increase airflow allowing a change to deliver more fuel and air to increase power.
To answer your question it is not necessary to install however you may be robbing yourself of extra power in this most used midrange.
I’m unsure if the specifics for the 150 so I cant answer as to sizes.