Petcocks jumped to the left at K3 or 4 (1973/4).
Agreed the pods are your running problem, along with the pipes (little to no baffling I guess?). A K0 airbox may be hard to come by. popping on decel is usually lean, but mid to idle circuit lean, not main jet lean. Raise the needle a notch by lowering the clip. Adjust air bleed screw (I think that's what you have) by turning in a skosh. That'll fatten up the low end.
After all that, the mains may be lean as well because of the pods and pipes. Even with a stock airbox, you may still run poorly with those pipes. So richening all three, idle, needles (mid) and the mains (top) may fix your running problems. CB750s aren't as sensitive to pods as smaller engines are. I think you can tune it to run properly. I run/ran pods (granted different carbs, Mikuni VM29s) and it ran flawlessly.