Thanks for the suggestions. Unfortunately I live in a metro area and have to work on my baby outside away from an outlet, so i'll have to get a battery powered dremel. I've linked two options below; would either of these have the speed/torque to shave rust/caked on carbon off the exhaust tips/muffler? Or conversely, is there any easier way i can take this gunk off without a dremel, that i'm overlooking?

Amazon.com: Dremel 8000-03 10.8-Volt Lithium Ion Cordless Rotary Tool: Home Improvement

Amazon.com: Dremel 750-02 Minimite 4.8-Volt Two-Speed Cordless Rotary Tool: Home Improvement

Much thanks.

PS. I've tried carb and choke cleaner.