[Talkwrench]

Yes if you move any more than 6 jets sizes from what is in it its going to be the wrong carb. eg; going from 66 down to beyond 60 just wont cut it . A bigger carb usually means its going to run leaner, and flatspot is a normal occurrence.. Now having said that if you do use the 450 it would pay to use a heavier secondary spring , I would guess the brown or the heaviest black spring, Its really going to only run on the primaries.