I just got my 400 sport back which is bored .50 over has a uni filter and hpd pipe and after riding all week i finnally decided to open it up to see how top end is and between half and ful throtle it bogs down bad and im guessing its the main jet but not sure how much bigger i need to go i have a 270 main and 40 piolet .

 

your pilot jet should be fine as long as it idles well and low speed driving is good.
When you say boggging down do you mean starving for gas or is it getting too much, if it is starving jump 2 sizes and go from there you want it as rich as possible without going over you may have to change your needle too but only as a last resort.