A hot plug will advance the timming, and it will help to avoid what is happening, I believe.
However, that is like a bandage, since the real problem seems to be insufficient load for the engine and excessive revs.

Note that OS recommends 13x8 and 13x9 props for this engine.
The attached graphic shows that the same engine works properly within the range of 13x6 to 15x8 props.

Please come back to us with the results of the bigger prop.