I done a quick search on this and found a couple of things but am still none the wiser.

I have a 79 12a bridgeport, with just the stock nikki carb & mechanical secondarys, It was running but now it isnt. Could some one please explain the ajustments on the carb, there are 2 screws, one above the other, the upper one smaller. These are for ajusting rich/lean, yes?? Where should they be set? they have both been fiddled with, at the moment the bigger one is screwed right in and the smaller one is almost right out. I've not had much experience with carbs before.

Thanks.

 

One of them adjusts how much fuel the engine gets at idle.

The other one adjusts how much air it gets at idle.

And unfortunately I can't remember which is which! Fairly sure the top one is the air and the bottom one is the fuel.

This is tricky! Raising the idle speed also makes the idle mixture leaner, since you are allowing more air in. You have to keep adjusting both screws.