1977-78 carbs brass idle restriction

With any luck your carburetor won't have those idle restrictions. They are small about .043 ,may to small with todays fuel. A easy to find drill bit 1/16 .0625 is big enough to enlarge that opening.

Black Arrow by that drill bit points to the last idle air bleed. It matches up to the bottom of the idle down Channel, Red dot. Now that is a giant mixing chamber, both idle down channels enter this same chamber and mix yellow line. Idle mixture screws or at the left and right side of that green line buy the purple X's. Now this is a really great system the older BBDs had totally separate idle system. Now the problem with this represented by that green line the gasket area is vacuum leaks. Even small ones will mess up the idle circuit ,both sides

That's the gasket in question prone to leakage because of the wide sealing area. Sometimes those two little short screws that come up from the bottom, holding the throttle plate to the Bowl. Loosen up causes vacuum leak. Tighten them back up sometimes you're good to go.

Older style idle circuit red dots separate top, New newer style on bottom. Black X's are the screw holes for little screws up from the bottom. There are little lock washers on those screws, which are now just flat new fresh ones may hold them screws tighter

No idle restriction

notice how narrow the gasket surface is in front of mixture screw

0.0295, normal stock item at least on line 7 to 10 days. If there's a Grainger in your town you can have that in two days. The 0.0310 Grainger going to have that one in a week The 76 77 78 79 mm bits long lead time at least 30 days. The fractional drill 1/32 should be available locally, and is not as easily clogged up and if partially clogged should pass enough fuel to keep the engine running. And it's not so big that it would be running Pig Rich all the time. With the larger air bleeds found on solid fuel carbs, .063 and 067 as opposed to earlier models .059 I cannot honestly remember if I used the .0310 or the 1/32 .0312 . Anyway there's the chart to look at .