Mercury 7.5 missing at W.O.T

[milfpig115]

Hello there experts I need some help with an outboard problem I'm having. I recently purchased a 1973 Mercury 7.5hp motor off of e-bay. I don't know the history on it other than the seller recently purchased it from someone else who said it ran fine. The problem I'm having is that the motor has a consistent miss when I run at W.O.T. The motor will spit and sputter and only run at about half speed. When I reduce the throttle to about half speed the miss disappears and the motor runs fine. Low idle is not affected either. I have replaced the plugs, had the carb cleaned and had the points replaced without a change in engine performance. Any help would be appreciated. I have checked all the wiring and found it to be in good condition. Thanks for your input.