Need help tuning a 273.

You should set the timing with the vacuume advance hose off of the distributor. Plug any vacuume ports on the carb. The advance hose from the distributor goes on the timed port. This port shoud be the higher of the two on the base of the carb. The lower is full vacuume and the higher one is timed. You can go to the the carb manufactures website and get instructions in PDF format to learn more. As stated it sounds like timing to me!

John D. Beckerley
Austin, Texas