Sounds like someone screwed up the incedence somewhere!

I'd strongly suggest that you try an 11x4 or 11.5x4 with a header and tuned pipe or moose can muffler on that Royal. Also, throw out that Master Airscrew. Try a Zinger, ecspecially if you spend the time to modify it as 3Dreaming suggests in the Props thread. You can also try an APC, though you won't get the response rate out of the APC that you would with a woody
Kevin