Reread your post and got to wondering....How long are your pipes? A lean carb can cause hot blue flames out an open header. Rich exhaust plumes are usually big intermittent balls of red or orange fire. A rich engine will generally rev up and run better, lean will snap and pop more the faster it runs, with a bogging moan when it runs right out of gas.
Just some idle thoughts on your problem, hard to tell what's happening without being there!