I have recently noticed that my newage 51 has a major power flat spot between 4750 and 5500 revs in all gears. I had a service in January this year and how only totted up 5000 miles.

If I hold the throttle down about half way I accelerate smothely up to the red line. If I push my 'peddle to the metal' the I accelerate up to 4750 and then there is no more power, the engine seems to struggle, and at 5500 revs it kicks in again with a jolt of power.

Any ideas what is wrong?