Qualcast 35s self propel drive speed too fast

[Steve2018 3]

Just got a Qualcast 35s that I have refurbished the carb on but wow the Self Propel drive speed is like a jogging pace and nearly pulls your arm out of the socket if your not ready for it. 

 

Is there a way to adjust the drive speed or do you need to adjust the drive speed by the throttle control? Only thing with that is the mower is near enough at idle for a slow drive pace or is that correct? 

 

Thanks