Welcome to the forum Robert and thanks for the video. Sure sounds like a misfire for some reason. 
At first I thought it might be fuel related since it does it at higher rpm but when you open the throttle it does not sound like there is any stammer like it is starving for fuel. Have you hit anything with the blades that might have partly sheared the flywheel key? Is it using anymore oil then normal?
At first I thought it might be fuel related since it does it at higher rpm but when you open the throttle it does not sound like there is any stammer like it is starving for fuel. Have you hit anything with the blades that might have partly sheared the flywheel key? Is it using anymore oil then normal?