I have worked on wornout chit my whole life, and have never seen a carb with a worn out throttle shaft, that couldn't be compensated for in other ways.
Shoot, I've seen garden-tillers with half the shaft gone, and still idled.
Think of it this way, as far as the throttle-shaft clearance is concerned nothing changed. The shaft has a certain diameter and the bushing a certain bore, and as far as the math is concerned, it don't matter where in the bushing the shaft is, the total difference in area is the same.
But what did change or may have changed, is the throttle blade position relative to the discharge ports and relative to the back wall. So now, instead of the air going past the discharge ports and picking up fuel, more of it is sneaking past the back side, and it is dry. So you just gotta compensate for that.
The primary defense is to just stretch out the first coil or two of that new spring and see if the sloppy shaft will drop home.
And if it comes to it, you can install a spring round the throttleshaft and pull it opposite to the primary spring, restoring the frontside clearance. The spring will eventually wear into the shaft so this is not a permanent fix.
So,
what has worked for me, is to close the throttle a bit to slam the door on the sneaking bs, then increase the fueling a tad on the front, and crank up the idle-timing a tad. Sometimes this results in a tip-in hesitation, if the accelerator-pump is lazy. If resetting the pump doesn't cure it, a bit higher float level probably will.
I could tell you about some other red-neck mods but something here should get you back in the ballpark.
