A carb that is to small will have a BETTER fuel draw. Because it will have a higher velocity at the venturi. It will have a better throttle response for the same reason. It MAY cause a power loss at WOT. The only reason that a smaller carb would cause a lean mix at WOT is if the jets are way undersized. With a new welch plug and my trusty micro jet reamers that wont be a problem.
P.S. Hogging out the jet under the needle won't make it rich. The JET (S) are in the venturi.
P.P.S. Hogging out the venturi is a bad idea too.