50TLR - Stalls when engage forward

I have a 2 year old Yamaha 50TLR that will occasionally stall when I engage the motor from neutral to forward. It starts and idles perfectly but as I move the throttle forward, the motor eventually quits. The only way I can get the boat moving, is to bring the prop almost completely out of the water. When the prop is running hard, I engage the motor forward and slowly put the prop down into the water. I have taken this motor into service 3 times and all they do is replace the carb kits and say it runs fine. I need some advice.

[boats.net]

Check idle rpm's, should be about 800 rpm's in neutral and 600 in gear.