David-1 en David-2 loom harnesses are not even and I don't get an even shed.

For David-3 there are separate instructions

If the shafts are not level, check and correct the following items as necessary

Insert the blocking pin	Look at this related article David - blokkeerpen
Check under the shelf that all cords run properly over the pulleys and correct if necessary. Check that all springs are the same length - if one has worn and is over stretched, this could be a problem and may need to be replaced.
Check the shaft cords The hook on the upper shaft bars must be connected to the first true loop next to the cut loop of the shaft cords. The lower shaft bar is connected to the texsolv cords coming from the lams.  Be sure to use the hole next to the cut loop. To keep the shafts in balance it is important that you always keep at least one heddle on the left and right side of each shaft
Check the lam connection cords Now look at the position of the lams - these are the metal brackets that connect the shafts to the treadles. Is the middle point of the cord exactly in the middle? Are the lams level? (assess this with the blocking pin in place)
The David 1 and 2 have spacer pins in the cords that run from the lams to the lower shaft bars. Some extra spacer pins are included in the spare parts bag. These can also be ordered as separate accessory (bag of 50 pieces, part number WA0222) By placing a plastic spacer pin in a loop of Texsolv cord, the cord is shortened by 1 mm. Always add one to both sides to keep the lam level.
Last, check the tie-up cords to the treadles The treadle tie-up cords for the David are 25.2 cm long (measured from the first to the last usable hole - marked in the photo below with a felt-tip pen = 21 cord holes). The loop where the cord is cut does not count. Use these holes when making the loop around the lam and connecting the treadle to the screws on the treadle. Make sure to use the screws that hang under the lam so that the cords run straight down. After tightening and with the locking pin still in it, the cords should all be at approximately the same tension. Tip : make marks on the cords with a waterproof felt-tip pen so that you always use the correct holes.
Loop around the lam through marked hole	treadle tie-up