I rebuilt my motor after it overheated and had to change to a 2MM overbore, Now I have to rejet the carb so it will run betterand have better throttle response. I know it had a #250 main jet originally so would I go to a #270 jet? Would that be big enough or would I have to go bigger? Maybe a bigger Carb? I don't want to go that way if I don't have to, the bike rides nice as it is but it is just the throttle response I want to improve and maybe a little more power. Can somebody help me? Any help will be appreciated!!! Thanks!!!

 

Ditch the roundslide 34mm and go with a 36-39mm flatslide carb. keihin makes a PWK36,38,39, and mikuni makes a TM36 and a 38. Flatslides will give so much more response and bottom end power.

Jetting may or may not have to be changed just from boring the jug .080. A fresh bore job can create better efficiency and cause you to have to jet down a size. Putting better reeds in can do the same thing and cause it to be rich. Get it broke in and do plug checks at part throttle and see what they are telling you. You might just be able to change the needle position and fix a problem like that. Your needle jet and/or needle could have wear causing running issues.

 

400 polaris's tend to be jetted to rich from factory in summer heat you could get away with dropping like two sizes to a 230 probably. do some plug checks wide open then, kill the engine and check. grey means lean. back is rich and a nice tan color in between is perfect.