The idle fuel feed tubes must be removed during an overhaul. A lot of crap builds up in the idle circuits, and they can't be properly cleaned without removing them. Also, the size of the tube's orifice is pretty small for a '77, so opening them up a couple of thousands of an inch will give you more idle fuel. The mixture screws will still allow for a proper mixture. Cliff Ruggles book goes into great detail on how to do this.
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1976 LeMans B09 Freeway Enforcer, 455/M40 Smokey
1977 Trans Am, 400/M21 Black/Gold Bandit. 44K actual miles
2017 Sierra SLT 1500 Z71 4X4 
2019 Canyon SLT Crew 4X4 
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