2gm20f

Hi there, anyone knows what this thing is and what it does. Going to change out the exhaust outlet and mixing elbow this winter, but this thing in the cirle coesnt look super great either and would like to do something about it, but .... have no idea what it is. :)

I would like to fit an additional starting relay as I'm tired of the "hit or miss" starting issue with my Yanmar 2GM20F. Could anyone share their setup wiring diagram with me? Much appreciated. :)

Lots of good work done. New prop shaft, shaft log, cutlass bearing and engine mounts. Reconditioned prop and strut. Refastened. I have more before pics and a vid if how bad the shaft and log were. May post later. Thanks for looking.

My 14yr old 1650hrs 2gm20f runs beautifully. Sounds pretty smooth. There's no black smoke but only slight white/greyish smoke. New exhaust and mixing elbows. Question is on long passage I'm seeing greyish bubbles that breaks to soot on water. Very little but noticeable. Should I be concern...