U may have an air leak, when u rebuilt it this winter did u split cases for any lower end work.? I was chasing jetting all over and it ended up being air leak from cases around crank, atleast i think anyway, everything led to that, when i revved the engine i would get a small amount of pressure on transmission side from vent, after i split cases i found it was assembled with no silocone or gasket, i resealed bottom and now runs better everywhere