similar problem, two different solutions. 1. Your tank vent? Open? 2. connections at both ends of the fuel line normally have small O-rings to make the seal. I have had a similar stalling problem when one of the o-rings was knicked. I am a little embarassed to say it was of my own doing. There is a tank end and a motor end, not interchangeable on my old Mercury 9.9. I did not know the difference and reversed them. That cause the on o-ring to get wangered and caused an air leak when a load was put on and revs came up.