If you are adding pod filters or a more open exhaust you might need to go up one size on the main jets. You can find the size stamped right on the jet. When you remove the float bowl its the part in the middle that hangs down low with an 8mm hex.
 
Standard sizes are 130, 135, 140, 145, 150, 160, 165, 170......
 
 
Fits 26mm, 32mm & 40mm BING Carburetors
Easy to replace
Sold each