Matt,

Are you still chasing a rich spot in the midrange with this carb?

Just out of curiosity, how far open is the butterfly held at idle (expressed in number of turns on the idle speed screw from fully closed)? Also, is there any sort of 'half round' cut from the throttle butterfly (near where the plate meets the inner wall of carb venturi)?

Depending on answers to the above, I may have a suggestion to lean out the 'fuel curve' of the carb in the midrange.

- Steve