It's been mentioned here that you should run a 4 stroke rich until it's broken in. Sorry, but no. You should ALWAYS run a 4 stroke on the rich side of peak performance, on both idle and high end settings. Even after many hours of running, a broken in engine can, and will toss the prop if given a lean condition, both on high end and acceleration. In fact, detonation is more likely to occur on a broken in engine due to higher compression/better sealing of the combustion chamber.

Cooler weather will increase the potential for detonation as well. If the engine was tuned to run reliably just shy of peak during warmer weather, cooler weather will put it on the lean side. Cooler air = denser air, which effectively means less fuel in the mix, resulting in a leaner condition.

I ran my Saito 150 all summer with no adjustments, set for "smokey" on high end with 20% lube in the fuel, and slightly rich on the low end. Cooler weather hit, and although I made the corrective adjustment to the high end needle, I neglected the low end needle, (My bad!) and while flying one morning I accelerated the engine quickly, and it shut down, loosening the spinner. Obvious low end mix problem, corrected by 1/8 turn richer on the low end needle.

I run just a DuBro aluminum conical hub/nut on that engine. Once you know your engine and how to safely handle it, have it properly tuned and can recognize the signs of potential detonation you can avoid tossed props completely, eliminating the need for multiple nuts if your application requires you to not use them.

Often the engine will "knock" or "ping" before it actually gets to the point of tossing the prop, giving you a good indication that it is too lean. This is a rather grey area, but when you know what your engine is "supposed" to sound like when it's running well, you'll notice these sounds. Obviously, on a reliable engine that has been tuned it will be due to borderline weather changes.

Pretty much, if you're going to run 4 strokes, you will end up tossing the prop at some point. Just stay behind the engine after starting, keep it pointed away from people and it will be fine. It's also a good idea to warm these engines up for a minute or so at idle or low speed before cramming the throttle to them.

Enjoy!