YellowHawk,
Loose the lock washer please. If it damages the prop hub it can fail and throw a prop at high RPM. NO fun at all when that happens
Also excess fuel can get into the cylnder and cause similar problems. Pull the glow plug and disconct the fuel line and (cover the plug hole with a paper towel )spin the engine well
making sure no fuel build up in the muffler as well. Always disconect the exhaust presure line when fueling to avoid this fuel problem.

You have probably already done his but remove the mold flashing from the prop. Ballancing the prop is a good idea too, it reduces vibration.
I read on this site years ago that a wide open 40 with a 10/6 prop has tips moving at the same speed as a 45 calibur bullet.