Spot weld settings

[Daz1968]

I have a clarke spotwelder and have success with the standard 120mm arms, however I have purchased some 350mm arms and are having issues with it blowing through, I know it's probably a setting I need to change with longer arms but can't seem to figure it out, I tried reducing spring pressure and it seemed worse, increasing it makes it better but not consistent.
Anyone have any tips in what should be altered for longer arms.

Thanks

 

[Daz1968]

Thanks will try upping the pressure, I wrongly thought longer arms would need less spring pressure, the instructions with spot welder are not exactly helpful tbh.