The vertical one should be the idle stop screw. Airbleed screws are almost always horizontal and they'll be near the front of the carb, in line with the air hole that you should be able to see in the middle of the front face of the carb. And yes, it will probably be on the same side as the carb arm. I'd have to go out to the garage (shop) to be 100% certain, but since it's New Years eve, I'm not risking the wrath of my wife by going to the shop tonight.