[Graydog]

Guess I should have clarified some things.

Seldom use choke in this hot weather. Bike starts and idles great without using it.

By warm up I mean while I put helmet etc. on. It doesn't actually just sit and idle for several minutes.
Well less than a minute I would say.

I drive it easy. A few fast starts but only when needed to get into traffic.

Air cleaner is spotless.

I'm sure it is running rich. I'm confused because both mechanics say no adjustment should be necessary.
Leave it set at factory settings (because the carb has not been touched.)

I think the key thing to remember is that I was getting 10 mpg better mileage before the holes were plugged in the exhaust. No driving habits have changed since then. The soot marks, the rich smell, and the lower gas mileage all appeared after the holes were plugged.

I may take a couple of the screws out just to see if it helps or makes a difference. Also I think I will try some carb cleaner before removing the screws and see what happens.