Also the previous owner had attached little slices of cardboard between the countermarch and the little plastic pins. This she said was to give fine adjustment on the length of the countermarch cords but I'm not convinced they did a lot of good.
So the upshot is that I put the metal rods back into the countermarch and basically took the whole thing apart.
I left the harnesses where they were but straightened and levelled them up properly.
I took out all the pieces of cardboard and adjusted the cords so they didn't need them anyway.
I levelled out the V shape that the countermarch loop cords make as they were all over the place before.
I detached the lams and started again to get them level.
I detached the treddles and retied them so they were near perfectly level.
I simplified the cords between the lams and the treddles so I didn't get met with about a million identical cords hanging down when I tied them up.
I tried to be methodical and get everything level while reading the instructions in broken English (the loom is Swedish) and decided that I'm better to follow my instincts!
I thought it would take ages but actually it was pretty quick and I really wish I'd done it sooner. I don't think I had the confidence before to detach everything and re-level all the cords for fear of making it worse.
Also I realised that a big mistake I was making - it sounds so stupid now - was that I was taking the metal countermarch holding rods (I'm sure they have a proper name) out too soon. I was taking them out before doing the tie up so as a result the treddles and lams were kicking out in all different directions.
This time however I left them in and took them out last and to my surprise everything stayed level and how it's supposed to be - balanced.
I checked the shed and it's much better.
Ah I'm so pleased and strangely it feels like I've finally taken ownership of my loom.
A question to the weavers out there - what is your preference on the treddle cords? On each project do you leave them all in place (i.e. hanging down from the lams) or do you prefer to remove the ones you aren't using? I find I get lost with all the surplus cords in the way but I suppose to have to retie them for each new project takes too long.