If you set the needles with low speed to lean you will end up with a lean engine at about 2 min into a race or qual. if you are pushing the car. The engine has to be rich on the bottom to keep the engine cool. If you richen the top in a effort to make a large change in engine temp to the engine you will slow the engine down as the top now will be to lean. The engines do not tun like a Nova engine or Sirio's They use the low speed needle to keep the engine cool. The engines normally will have a larger idle gap then any others due to the rich low speed. This does not at all mean that the engine should be stumbling rich of the corner it should be crisp and smooth with alot of smoke like I said earlier. If you are stumbling rich on the bottom then do as Sean stated above and lean bottom and very slightly richen the top. And I mean small amount for the top needle.