Midrange sputter/bog

I’ve been trying to resurrect my old Ruckus, found a good deal on a '16 stock GET. Put a generic PZ16 on it. After swapping the stock 35/75 jets for 38/78, it starts and idles fine, and runs great at full throttle. The only issue I’m having is that, sometimes, at about 1/4 throttle, it sputters and loses power. If I give it more or less throttle, it smooths right out. I’m thinking a needle-clip adjustment might fix this, but I’m not sure if it is more likely caused by being too rich or too lean.

This is kind of embarrassing, at one time I would have known, but old age takes a definite toll on memory (I’m 67 now).

Can ya help a brother out?