my carb is a 75-77 and i have the needles for the pre 75..........
Incorrect Primary Metering Rods
Results in: Poor idle, rich idle, ineffective idle mixture screws, surging at cruise, poor mileage, poor cold-running characteristics, hesitations off idle and/or at cruise, poor manifold vacuum with resultant ancillary problems.
Comments: In addition to seeing incorrectly sized metering rods for the application, I am also seeing carbs with the WRONG rods installed. Pre-’75 (up through ’74) Q-Jets use metering rods that are approximately 2.47” long overall (total length from the metering tip to the extreme top of the rod). 1975 and newer Q-Jets use rods that are about 2.40” long. The early rods typically also have just a plain number stamped into them (like, “44”), or will often have the letter “B” after the number (like, “44B”). The later rods will often have the letter “K” or “M” after the number. If an early rod (long rod) is installed in a post-’75 carb, the actual shank (body) of the rod will be stuffed down into the jet, resulting in a severe lean condition with associated marginal drivability. Likewise, if a late rod is used in an early carb, there will be virtually no lean-out from the power piston at idle or cruise, and the carb will suffer a severe rich-running condition.