[C320-list] Removing carbon from exhaust port

[nibj]

I have a ’95 Perkins Perama M30.  I had to remove the heat exchanger due to a leak, and I now notice that the aft most exhaust port on the engine has some carbon coking deposit  around the circumference (the other two exhaust ports are very clean).  It is not close to blocked (I don’t have exact figures for the percentage).

So I have two questions that I hope you can help with

1) What are possible reasons that one port has more deposits than the others?

2) I could put a small wire wheel on a drill and polish some of the port.  Would this be a good idea?  Would the carbon particles risk falling into the cylinder and cause damage?  Should I just leave well alone?  I don’t want to remove the head!

Thanks