5 spot it sounds like the front bearing seal is bad. I had an old junk Leo that did that. It was just plain a junk engine. I would take the prop driver off. It should have a woodruff key or a brass cone under the driver. You may have to pull on the driver with some pliers. Not real hard just enough to disengage the brass split collar. Check the front bearing visually for damage. If that fails Pull the carburetor and back plate off and inspect for debris. I had some foreign material in the crankshaft under the carb cause this symptom once. If you see nothing or a problem, and the engine is under warrenty send it back for repairs. I Hear the warrenty situation is very good on the Evo engines. Good luck with your engine.

Mark Shuman