Xs 400 rejet

I have a 1982 xs 400. Cut off the exhaust short and have open air box. I want to know what I should rejet the carbs to if anyone has any idea

Post pics of what you have. Cutting off mufflers and running open air boxes is not going to improve anything just make things much worse for tuning. Hope your mufflers were bad and not a good set as good stock ones are hard to find and will give you the best overall performance for these bikes. As for jetting there are no specific sizes for modified systems as a lot of it has to do with what mufflers and air intake you changed to.