I have had on a few occasions, a loud squeal coming from my engine, with no power and the tach reads about 700 RPM, even though the engine is actually revving much higher. 
if I back the throttle off and then put power back on, two or three times, it actually all seems to work fine. I'm wondering if it is just in need of a new belt, or if possibly there's some oil / Residue getting onto the belt?
One time I took the engine cover off and actually wiped the belt down with the dry cloth and it seemed to work. I know there is a little discharge hose coming off the engine and it runs down the starboard side into the engine compartment where there was also some splatters.
Just wondering if anyone else has had this happen, and what they did to resolve it. Obviously the first thing I will do is change the belt and make sure that hose is for the oil discharge is not flopping around and spraying it towards the belt. I would appreciate any suggestions that you may have, take care, 
Rich