Im told that a common problem with Tohatsu 50hp's after a few years is the middle coil going. The symptoms are that after running for a while when the engine gets hot you loose power. This means that the engine will not run in idle/tickover and stalls in neutral. I had this intermittent problem for years as I dont use my engine that much but the final straw was at the end of the cross channel mission.
http://www.rib-shop.co.uk at the end of the river hamble was the source of this diagnosis