Fuel starvation?

Question
Bert, our 90hp '97 Mercury 3 cylinder, 2 cycle engine will run at around 4000rpm for 20 min or so and then dies.  It seems like fuel starvation.  We've checked breather line, vent on tank, changed water/fuel filter, checked fuel pump.  What else would you suggest?  We can always restart and run indefinitely at about 2800rpm but whenever we try to speed up it dies.

Answer
Hi Wendy    Did you try changeing the fuel line from the tank to the motor?This sometimes can be a trouble area.If it is  of the type that has a fitting that connects to the motor the o-rings can go bad and allow air to be drawn into the line at high fuel demand(speed)Their are also other  things that could cause this problem,other than fuel.