My 1986 40hp Evinrude has been rebuilt, new pistons, carbs cleaned and checked, new thermostat, and a general check of everything mechanical. Rebuilt because pistons, especially the top one were badly burned. The motor now runs well at partial throttle, but stalls when trolling for a few minutes, and then is hard to re-start. Thought I was going to be towed in yesterday and its bad enough that I'm reluctant to go out on the lake.