Ah... The old MD7A. 2200? Get the revs up to 2400 - 2600 and that may take care of some of the sooting problem. It always seamed to wash off well enough with just soap and water scrubbed lightly with a washcloth.
I had a lot of cooling problems too and had to back flush the motor on a couple of occasions. At around 500 lbs., she''s a heavy motor with casting thickness to handle seawater cooling but the water jackets and ways are a tad small so they tend to block up easily.
I guess I took care of the problem once and for all and evicted that patent thing from my bilge along with all of its superfluous paraphernalia. Then I hung an outboard motor on the stern and life has been wonderful ever since!