Engine speed should increase smoothly from 1750 rpm at idle, to its maximum which is probably 3000 rpm flat out. If it rises above maximum anywhere in between, the governor isn't working properly. It's a very simple mechanism - just an air vane beside the flywheel fan, and two springs on a tin plate. I suggest you look at it carefully, and if possible post a photograph of the tin plate and springs. Bruce is the expert - he can normally tell people what is wrong very easily.
