Hello again I have had a few thumpers,I currently have an 83 XT550K with YDLS. 1 carb 2 carbs I understand, But a carb and a half I dont understand. Can someone give brief explanation or point me in the right direction? Thank you for any help Crash

Before they got cute with the carbs on big thumpers they cheated.

The primary carb deals with starting the engine, idle, and general running around. This gives you good torque and fuel economy.

The second carb is not connected to the throttle directly it works on vacume from the primary carb and opens when the engine vacume demands it, Generally at higher rpm. Therefore you effectively have a whopping great carb when the engine can handle it and a little tea strainer when i can't.