20hp Johnson dies after a while at low rpm

[SwedishDan]

I have a ‘87 20hp Johnson that runs great at higher speeds. It’s usually easy to get started as well. But when I run it just above idle, it just suddenly dies on me. Something it runs fine for 30 minutes, sometimes 3 minutes. Not consistent at all. But what is consistent is that it’s always very hard to get started again. It takes 5-10 tries at the starter before it gets going again. Whats most likely to cause this?

 

[racerone]

Test run with another tank and hose?----Is the water pump impeller in good condition ?-----Does operating the manual fuel pump help?