Stumbling 50hp Yamaha Pro

[Planepilot]

I have a 1987 Yamaha Pro 50. I have rebuilt the carbs twice and changed out the plugs. The engine idles perfectly. The mid and top range is smooth and powerful. Once I start to bring the power up above 1200 rpm the motor stumbles and hesitates. As I bring the power up above 2000 rpm it smooths out and runs like a top. I can't figure it out. Any ideas? Could it be my prop?

 

[Bobg]

Make sure the 3 little hole in the calibration pocket are clean and open, that's where the 3 little holes are that your throttle plate passes as it opens, and also run a fine wire up your pick up tube in the carb, to be sure it's wide open.

When it stumbles, try a little choke/primer, and see if it picks up better. That will tell you better if it is actually your carb being too lean though the idle to off idle operation.