Yes, the stock carb causes the mixture to go lean at midrange. This was on the 1st version of the carb, the latest manufactured carbs have a modified spraybar that is supposed to help the mixture problems. The 1st version carb can be modified by drilling an air bleed hole in the carb face in the appropriate spot, then opening up the low-end mixture screw. This helps the mixture to be richer at midrange.