Thought I would share this and maybe save someone some head-scratching. Tuning my 1979/301 carb modded for the 455, and was getting a prominent engine miss while holding RPM around 3k or so. Sounded like a carb issue, so I bolted on my 72/400 carb, and works perfect. Tore the other carb down, blew out the passages, etc, installed a new gasket and tried again. Same problem.
End result was that the air coming off the mechanical cooling fan blade (i usually ran an electric fan) was catching the choke flap, causing air turbulence and a bad running engine. Shielded airhorn from the fan air (or just put the air cleaner on), and problem gone!
My 72 carb does not have a choke flap, so I assume was not catching as much air as the 79 carb...
Anyhow, thought it was worth sharing!
