Fuel starvation possibly, check for collapsed lines and/or a defective pump. Check if you spray fuel in the carb opening if it will keep running. Some of the passages in the carb are very small and hard to clean out, could be internal blockage.
I have completed a refresh of my 1965 Evinrude 40hp manual shift, automatic choke, electric start.
New ignition system.
Replaced thermostat and impeller.
Before I started this, the last time it was out it cranked and idled fine. As I was pulling away from the dock, I accelerated and it died, not to start again. Pulled her from the water put her in the barn and she has sat there for 6 yrs until this March.
Updated a lot on the boat. And started on the motor yesterday.
So, I have done everything listed above yesterday and today. Early up late to bed.
This afternoon I tried to crank it. It starts, idles rough. Dies. I give it a little throttle it speeds up then dies.