Hi!
Are you sure you don't run the engine too lean?? Factory settings are just a way of getting an approximate setting ...not a way of obtaining a GOOD setting!
You have to listening to how the engine sounds at full trottle and set the high speed needle a little rich. Then hold the model straight up and check the rpm. It's vital that you always run your engines a little rich in this position.
A much better prop thanm a 10x7 would be a 10x6 or 11x5 APC.