Note the barrel with a setscrew. Now, note that when the spark advance is at full advance, it bangs up against a projection on top of the cylinder block. Now that you know those two things, advancing the throttle control will first take it to full advance (against the projection), THEN, and only then, should contact be made with the barrel/setscrew. If not, loosen setscrew and slide barrel on rod to adjust. NOW, further advancing the throttle control will kick the carburetor to WOT.