Not sure on the 450s but in 2 strokes when you go big bore you are sucking more air which vacumes in more fuel so you jet leaner. Not sure if this is the case though. Like posted above it could be a different jet kit that uses different numbers, Is the main a hex head jet or round with a screw driver slot?
"Let me ask you this: A guy breaks into your house, but you don't have a gun. How are you going to shoot him?" Dale Gribble