I have been experiencing occasional (twice in last year) situations where when its really hot (95 degrees) and I run the boat, moor it for an hour, and then run the boat again one engine dies of fuel starvation. Yamaha customer support clued me in to looking at the primer bulbs, and the continuous wave web site had an article that confirmed my suspicions that primer bulb orientation matters. I finally (hopefuly!) traced the problem to the primer bulbs having a horizontal orientation. In fact they were oriented with a slight downhill slope, when referenced to the fuel flow direction. The check valves need gravity to operate so if the bulbs are pointed downhill the valves will stay open and allow fuel to flow back into the tank and air to get into the fuel lines. The result is the engine dies of fuel starvation. So moral of the story - check the orientation of your fuel primer bulb and make sure the fuel flow arrow is pointing skyward.