Controlling motor speed with GRBL v0.9 Woodpecker.

This is my first post and I am only just finishing the setting up my 3018.
The woodpecker board is working OK except for motor speed control. The kit came with a rather cheap looking black plastic 24V power supply.
When I ran up the machine, the spindle speed never exceeded 1000rpm.The controller would reduce it but not increase it.
I played with all the settings that I could find but whatever I set, the speed topped out at 1000rpm. I noticed that every video I watched and a number of other suppliers of the 3018 used a much more substantial regulated power supply so I have just installed a Surom 24V 15A Dc Universal Regulated Switching Power Supply 360W.

Set to 24v it made no difference but if I adjusted the voltage to its maximum of 31v the motor speeded up considerably but the GRBL controller did not show the change and the slider would not change the speed. Now the controller will not change the speed at all. The only way I can stop the motor is by unplugging the power supply. I have not changed the wiring. I tried Candle but that did not stop the motor either.
I am controlling the Woodpecker directly with a W10 PC and plan to continue to do this as I have a spare in the workshop and have no experience of Arduino or Raspberry Pi.
Any help including a reco to change the basic config of the project would be appreciated, I have no prior experience of control software or hardware but am very familiar with Windows and PCs.
Gcode file is attached.

Thanks all.

 

Thanks for your help guys