I bought a used white brothers e series exhaust for my 01 400ex just wondering where to start on jetting?I want to keep the air box closed and run all the disks in the exhaust.The stock main jet is a 148.I was thinking 155.

 

I have a # 152 in mine but thats out here in west texas @ 2600 ft.

 

I would call their tech line and ask them. They should be able to tell you with consideration to elevation, temp and such.

 

The 155 main jet did the trick.