I've been running around my local resivoir with my recently acquired 1990 Evinrude 9.9. I usually vary my throttle, but a lot of the time I'm at WOT for 10-15 minutes at a time. Is this bad practice? I can't help it, its too much fun going fast!
I ran my 35HP WOT at every trip almost for a couple of years. I sold it and another guy does now. They carbon up much less. If its propped right I dont think it hurts anything at all. Just baby it with a good oil.