intermitent spark...good external coils

[mr bill]

1985 johnson 50 h.p ( twin ) running at 3/4 throttle , lost power to 1/2 . checked with timing light, intermitent spark , pulled flywheel and the key was broke.....replaced, and still runs only at 1/2 speed. completely cleaned the fuel system....checked reeds.......still runs at low speed, give it gas and runs with a hollow sound , and dies..........switched outside coils, same problem...maybe power pack ?????