your running lean right? now matter how much you richen it still act's lean? I see 2 probable causes... by locating the header tank where you did you effectively moved the tank away from the engine... sounds strange since your header tank is no farther away than the main tank right... nope the engine does not see it that way... it's still looking at the main tank as it's fuel supply, only now it's MUCH farther away because it has to travel through more hose and a tank before it gets to the carb. In the pic's it looks like you could mount your header between the main tank and carb... that would be the best spot. the other thing is the header tank center line is lower than the main ...the main is already low, you want your main tank centerline about 1/8 inch or so below the carb centerline... moving the main tank is not worth it... it's not that much lower HOWEVER your header is lower than the main... not good, you want the header centerline to be up closer to the carb centerline... about 1/8 inch lower if possible.

John