I have had to weld a small block of steel to some part, can't remember exactly so that it put more pressure on the adjuster spring and that solved the problem with it dropping down, that was on a Honda but pretty much the same setup. As for cutting too low check that the blade carrier is up inside the body and if this is ok then it must be a problem with the height adjuster arm to the front wheels or the front axle bushes have worn out or disappeared
