This may not help, but the last time I did this sort of thing... the same thing was happening to me.... if I'm following what you're saying.

After everything was assembled & tightened, I had all the 'slack' adjusted out of the throttle & return cables, the way I like em, but... the throttle wouldn't return all the way.
When I backed off either cable just a little... the throttle returned as intended. I 'played' around with each cable & got the same results.

Another thing I was thinking you could try before removing the powder coating was…
1. See if the throttle grip spins freely on the end of the bar.
2. See if the throttle grip spins or rotates inside the switch housing W/O the throttle cables attached to the bottom housing.
...Install the grip in the housing on the bar & tighten the housing bolts
...Test the rotation

 

I disagree with your disagree. I just went through this with my Kodlin bars. Had them powdered and I thought it was just the powder as well. My grip without the controls wouldn't spin freely. I sanded it down till it spun freely and though it was good to go. I Put all the controls on and stuck all to hell again. Nothing I can do to fix it. I took off the plastic piece for the throttle lock and it spun free again with the controls all together. What I had to do is take that little plastic piece off of the throttle lock and grinded it down till it worked. Now the throttle works and so does the throttle lock. I guess depends on the brand. Mine are some ebay knockoffs of the WCC knurled grips.

 

special ed i was readong a old post on your fender what size tire and what brand how much did you lower your bike. i have a 05 fxdc and was looking at doing the same thing just wondering how to make the rear fender look as good as yours. thanks

 

Wow, way to go off topic on your first post!

Special Ed:

I had the same problems when I put on my HD nostalgic grips for whatever reason. I put some grease inside the grip, and pulled grip out a little and tightened the controls and it worked out fine. If the grip sits all the way in on the bar, it will bind and not spin freely. Maybe try that before you get to sanding? The grease worked well too.