New to me 2014 Honda BF30D-starts but only for 3-4 minutes

It has had very minimal use in its life, like maybe 50 hours. It hasn't really run much in the last year either. Last time was about 6 months ago. I tried to start it yesterday. Oil looked very clean. It wouldn't fire up so I changed the gas and fuel separator and then it fired right up. It runs for about 3-4 minutes and then an alarm sounds and it cuts off shortly there after. Previous owner says he changed the impeller last year just before I got it, so about 12 months. The water coming out is strong and cool. I'm stuck. Any advice?

Thanks!!

What does the thermostat look like? The 50 hours, was it run in salt water?

I haven't pulled the thermostat yet. It's only lived in salt water.

If this like some of the "salties" I've worked on (that were very poorly maintained/never rinsed after each usage) you may be in for a very thorough cleaning of ALL water passages. This could involve pulling the lower unit for a water pump inspection, or maybe just an entire replacement (where I would start). From there to the t-stat housing, which, if all crudded up internally may lead to the exhaust/water jacket cover removal for a cleaning of the passages there - and then the head, for more cleaning/inspection.

I would start at the pump to verify, beyond any doubt, that it was solid/ready to go.

I would be removing the exhaust water jacket irrespective as Alan said or you will be having problems at a later date. Make sure you grease the bolts and seal when you reassemble and have a new anode on hand too.