Picked up a Nissan 9.9 HP 4-Stroke. Carb is absolutely clean, new spark plugs. Took the carb apart and made sure all the small orifices are clean. Starts right up on first or second pull. Idles great. BUT misses badly at higher RPM. Changed out the coil with another one. Same issue. Pulled the flywheel to be sure all is well. Plugs look black and sooty after running at higher RPM's. CDI unit???