carb jetting for r&d pipe

[st.clair.jetski]

so my buddy bought an r&d pipe for his 750 sx he is running a single 46mm mikuni he called r&d and they told him his main jet needed to be a 130 since his main jet with a stock pipe was a 150 or sumthing his is skeptical of dropping that many sizes any idea on how he needs to set up his carb