Yesterday I pulled the carb. It's a round slide 34mm Mikuni, from Sudco. It's a Royal Enfield setup from Sudco. I just talked to a Sudco tech in CA. The only difference between what I have and their standard RE setup in my main jet. Their's is a 210. Mine is a 195. All other parts are identical to Sudco's standard setup.
I'll be ordering a rebuild kit. When I opened the float there was something that looked like parmesan cheese in there. Any clogs in the internal air passages could make it run rich. I'll order the 210 main, just in case it takes one to get it right.
Here's a post from ACE. It's about the Mikuni flat slide. The numbers are different, but I have a round slide.
It's better that I rebuild this thing than just fiddle with the air screw. Every one here is so willing to help. Better to get done right from the inside, then ask questions.
Here's some of the gunk.
Here's ACEs post....
I would say that a 30mm or 32mm Mikuni would be fine. In fact, a 32mm Mikuni Flat Slide carb is what we normally recommend for all Bullets, but we are taking into account that they will stick with the one carb as they upgrade their power levels. IF you have no power upgrade plans which include increased breathing of the cylinder head, then a 30mm would do fine.
You'll need to re-jet any of these carbs, because they come jetted for other bikes which are not like ours.
30 pilot, p6 needle jet, 190 main
would probably be a good jetting start for a stock bike and a Mikuni TM32-1.
Pilot jets are 22/210 type
Needle jets are 389 type
Main jets are 4/042 type.