subaru engine will not rev up when attached to the mower

I have a deutcher mower with a Robyn YD 23 7 hp engine on it The last time i used it it worked OK but now when i started it the engine will not rev up beyond half by but when the engine is disconnected from the mower it revs up ok

I have tied to fix it by

1 cleaning and then removing and replacing the air filter
2 Cleaning the carbi and the main jet
3 Checking the timing key-way and the screws on the coil
4 Replacing the spark plug
5 replacing the ignition coil
6 Changing the oil
7 cleaning the head of carbon
8 reseating the valves resulting greatly increased compression
9 replacing the fuel with new clean fuel
10 cleaning the fuel filter
11 replacing the head gasket


with all of these the engine still wont rev up but the butterfly is in the full open position when it is attached to the mower
The only thing i have not done is pull the engine apart to check internally workings

Can anyone assist with this issue

Sounds like the govenor is out of adjustment.
The throttle cable stretches a spring which holds the butterfly wide open untill the engine starts to turn when the govenor shuts it down to maintain the govened speed.

Thanks but i manually activated the governor but no go still not reeving up