I agree more information is needed, but keep in mind that if you decide to re-power a Atomic 4 with a diesel
it could easily cost you $10K plus....
The Atomic 4 was a good engine
in its day, but they are getting pretty old. Parts
still available, but getting more expensive every year. The fresh water
cooled engines do run better than the raw water
I went all the way on mine, electronic ignition & electrical fuel pump
. It still took up way too much of my time.
Re-powered my boat about 7 years ago with a Beta diesel
, could not be happier, more sailing and less swearing.