On a efi 4-st. if you put a pipe or anything aftermarket on, you now have to bring your bike to a dealer to reprogram the computer,according to my pal that worked for KTM with the factory race teams. So on a 2-st. if you do a minor mod like reeds,you have to take your bike to a dealer for a reprogram,this includes pipes and silecers,etc. and porting the cylinder could be out of the question all together. Because the computer may not be able to come up with a program , that doesn,t cause the bike to blow up. IMO where better off with carbs.