Sticky accelerator cable.

[Dead Parrot]

From the pic, it looks like the flare at the rear of the plastic tube might be binding on the metal bracket for the trans shift cable. If your trans doesn't need that shift cable, might bend that part of the bracket a bit to give the throttle cable more clearance.

My Eddy 1405 has the throttle cable in the same hole as yours but due to a 1" spacer, the trans shift cable is on a separate bracket so I don't have any bracket/throttle cable interference. The return springs run from the higher hole on the carb to a homemade attachment point forward of the carb.

Edit: looks like your return springs are just like mine based on your last pic.