this question is for people that own a 400ex w/ a t-4 slip on....what size jetting are you running???....i think i may need to rejet

 

Call the company you bought it from. They should have the answer for ya. We just put a WB E-series on my sons 400ex and had to go to a 160. But we might live at a different elevation that you do. But I would say, 160 or 165 should work.