[chopper]

CobraEd is correct. The carbs equipped with vacuum secondaries do not have provisions for the secondary accelerator pumps which the mechanical secondary carbs have. I understand that the carbs can physically be outfitted with mechanical linkage, but will suffer from severe bogging when the secondaries are opened. I think the only practical solution, if you really want mechanical secondaries, is to replace the carbs with mechanical units. My $0.02