Best way to clean intake passages?

[Sparky]

I’m in the middle of a valve replacement job and before I fit the new valves, I’d like to clean out the decades of black buildup in the intake passages. It’s black tarry stuff about 1/16” thick.

Is there any chemical that would easily dissolve it? If not, what’s the best method? I have a small dremel tool as well as an air-powered die grinder.