I talked with Oscar at Alpha Carbs in CA, who clearly knows his stuff. He's going to rebuild the carb, including bushings for the throttle butterfly shaft, and return it to me the next day. Very reasonable charge.
In the meantime I'm going to take a closer look at the linkage rod I had to fab because of the dual exhaust I installed. I don't *think* it's too long and/or restricted in its travel but I gotta get this part right.
