The cutter will be experiencing loads not only in the standard arm saw front and back (Y) direction but from side to side (X) as well. Arm saw's bearings are made to handle Y well enough, but the X is frequently loose. Hold the arm saw's blade and push it from side to side, you'll probably find quite a bit of slop there.
The lift back-lash is probably in the nut and the end bearing, if there even is a bearing at the shaft's end, and some saws use two bevel gears in the mechanism for even more play...disassembly required.
Sorry ‘bout the redundancy... Phil posted while I was writing this
