The rear screw is idle mixture. Turn clockwise all the way in and back it out 1 1/2 turns to be in the ball park. Clockwise = lean CC = rich. The carb in the picture has an adjustable main jet. Turn it in clockwise all the way in and back it out two full turns. You should be a little rich so you'll have to dial it in from there. Clockwise = lean CC = rich. My idle is at 1 1/2 turns out and my main is at 1 3/4 turns out. But I'm at sea level in Seattle you'll probably wind up a little leaner where you are. Turn the main no more than 1/8 turn at a time so you don't lean it out too much and do a plug chop to double check it. Most factory Bendix carbs were a Fixed main jet design and just had a plug on the top of the carb. You had to change the main jet to dial the carbs in (a real pain). It's a good dependable user friendly carb.