And or the prop is to much and is killing the carburator suction.
Quick check-- put on the smallest RECOMENDED size prop. If the response is razor sharp, you know you need a smaller prop.
Another check for too big of a prop. Flip the plane vertical at WOT. It should not sag in RPM at all.-------Go to smaller prop.
I think propsizes are picked by a sales man at some companies.