Run up fine but stumbles at 5000+ RPM
The next day I replaced the spark plugs and again everything was fine until going over 5000 RPM. If I throttle back it will sometimes clear itself at a lower RPM without stalling but this is not immediate taking perhaps 30 seconds before it runs smoothly.
I have attached a picture of two plugs, one removed at 100 hours and the second removed since the problem developed at 188 hours. The bottom left plug with the beige deposits is the 100 hour plug while the upper right plug with the black deposits is the plug removed after a dozen tries as mentioned above. All 16 plugs are showing the same characteristics, eight beige (100 hours) and eight black (188 hours).
The black deposit makes me think (in my infinite ignorance) that the engine is flooding. I checked the chokes several times and they are indeed going to the off position.
And a special thanks to my engine for quitting at 0 feet instead of 300 feet. My landing options are trees or water.