Black soot ok plugs

My slanty is a 225. It does not like 11/21. It runs much better at 13/23.
yBlack soot inside the tailpipe is not good.Tan plugs is vert good.These two do not usually appear together.
The slow idle seems to indicate a mixture problem; but could be a slipped timing issue. If there are no other driveability issues, such as powerloss, stumbling,etc ,this is what I would do.
Fill up with fresh gas, recheck the timings, make sure the choke is coming off in a reasonably short time, make sure the choke pull-off is working and that the vacuum break is correctly set, and check for vacuum leaks. Then roadtest.
If you still have problems, I would increase the valve lash to .013/.023.
Oh yeah, check to be sure the float-bowl vent is open.
If you still have problems, revisit the fuel level.