2000 70 hp yamaha 2 stroke outboard

[wallaguy]

Please help i have a 70 hp 2 stroke yamaha non-tiller
the moter starts up fine i let it warm up before takeing off
it rus good
when i give it full throttle i can get it up to plane
for about 6-10 seconds then i lose all power and it dies
it will be hard to start after that once i get it started it runs fine half throttle no problems full thrittle same thing happens
i have replaced
the ball
new gas line
plugs
fuel filter
i even used my brothers portable gas can with new gas and his ball and line same thing happens
with ear muffs on in driveway it rus great
only happens in lake
i have had it at 2 dealer ships nobody can get it fixed
boat and motor still like brand new
please help

[boats.net]

May need to remove and clean carbs and fuel pump. Could have an ignition problem, might need to get ignition tested.