1977 kz650 pods and open exhaust... Base thoughts?

A general rule when changing to 4to1 and pods is to up the main jet by 3 and the pilot by 1. That is just a starting point, you may need to increase or decreas the main depending upon pipe flow. But you first need to get the needle setting correct.

You do not indicate if you are using the stock carbs or not, but IIRC the stock carbs are vm24ss and came with 102.5 mains and 15 pilots. So a good starting point would be 110 mains and 17.5 pilots. I do agree that issues with mid throttle are most likely a needle issue. Since you get a stumble just before 1/2 throttle I think it is just a bit too rich. Try leaning the needle by moving the clip up either one notch or shim it a half notch. It that does not solve the issue you may need a leaner needle.

Step 1: DETERMINE THE CORRECT NEEDLE AND OR NEEDLE JET.
Whether or not your carburetor is a MIKUNI or a KEIHIN, it does not matter. This is the most important step in jetting your carburetor--period!
1. Remove the main jet.
2. Place needle clip in mid-position.
3. Start motor and run it on the stand.

Condition: Motor running and main jet out. Needle or needle jet is correct: Carburetor should run clean to approximately 3/4 throttle. From 3/4 throttle to full throttle, the motor should start to break up as a result of too rich condition.
Correction: None needed.

Condition: Needle or needle jet is too rich. Carburetor runs clean to approximately 1/2 throttle but breaks up before 3/4 throttle as a result of too rich condition.
Correction: Mikuni replace needle jet with next leaner and test again. Keihin replace needle with next leaner diameter and test again.

Condition: Needle or needle jet is too lean: Carburetor runs clean beyond 3/4 throttle and has an erratic throttle response.
Correction: Mikuni replace needle jet with next richer and test again. Keihin replace needle with next richer diameter and test again.

The emphasis here is to find the correct needle or needle jet diameter, which will allow more fuel to pass than is needed but not so much that the needle itself has no control below 3/4 throttle.