i have a stock 400. i just upgraded to a aluminum air box, twin air filter, and white bros e series pipe. what jet do you think i should run. I am in michigan and plan on racing. any info would help thanks for your time in advance

 

call white bros and ask them or call any local shop cause we dont know the alt. there
thats what i would do any way

 

Try a 155 main and 45 pilot. Play with the fuel screw some. Check the plug, don't run it lean for too long. Even though the carb has an air cut-off valve for when the throttle is chopped, it will backfire when too lean.

 

i would say try the 155 main too......