black smoke
having problem with tow rig. 350 chevy engine, single plane intake (i know its not perfered for towing) holley 600cfm with vac. secondaries manual choke, in a 74 gmc 4speed manual. Had same problem with 750 vac. secondary, this 600 carb came off a good running 454 about a year ago Smokes black while driving, could this be a power valve problem
? Vac. advance seems to be working, choke is off. any advise appreciated.
Ryan