I recently had my 95 GSR (of which I am the original owner) to the shop for 90K service. The timing belt and water pump were done.

A few weeks later I noticed that the inside of the exhaust pipe tip was starting to show some carbon build-up, as if the engine was burning rich.

Previously the color was always a very light gray, almost nothing there at all.

Can a timing change result in this carbon build-up? I'm wondering if the guy who did the work might have adjusted the timing differently than it used to be.

I appreciate any insight y'all might have.