One of my customers alerted me to the fact that our kit for these does not include the main jet o-rings. They are not shown in the parts book but are in the workshop manual.

I can size them if I can get the dimensions of
1/ the ID of the groove
2/ the height of the groove
3/ the ID of the bore the o-ring fits into

http://litetek.co/Carb_Kit_Suzuki_GSXR400_GK71.html
cheers
Blair