Have twin Yamaha 2 stroke 2002 150's. When running about 4000 rpm for 10 minutes or so one of the engines and they seem to take turns drops down and the primer bulb flattens out. They sat for about 3 years, rebuilt carburetors, replace all gas lines, new filters including the hardware twice, new primer bulbs, sometimes they will run a bit longer, opened up gas caps while running and no help. Just had gas tanks cleaned and all fuel removed. Took it out and the same thing. I have also checked the pick up screens and there is also no check valves in either tank. Separate tanks.
