The more pressure you have in the reg, the harder it is for the firing valve to open. If the firing valve cannot open, you get not air going down the barrel.

I have never opened a Walham reg, so I can't really advise which way the screw should be turned but you need to seriously reduce the pressure in the reg.

The springs should have some grease on them, most people use the same grease you would use in a springer as it needs to be completely non flammable.