A flexible screwdriver Its shaft is "wire" and can bend almost 90 degrees, so turn handle horizontal plane, but tip is vertical (or very close to it
. You can chang to whatever kind of bit you need also, on the driver end. Very handy. They make a flex bit for drills also, you can use if you have one already.
The idea Spud suggested works well also, ie loosen the bands on the manifold, rotate carb, then adjust screw, and rotate carb back to vertical before testing. IT MAY run very rich, if the bowl dumps fuel into intake tract for a minute or so (or be flooded/hard to start for a few minutes).
There is a CHANCE the floats on both carbs are too high, and dumping fuel when starting out and or braking or tilting the bike from side to side at a stop. Try that (tilting the bike) and see if it stalls. Thats the way to find out re floats (one way w/o dissaasembly of carb).
If its floats, I can explain setting them for you as well. (Spud may have this covered already in his thread...)