OK then,,,,
On the air filters, not sure, the more the air filter is blocked up, the more the mixture is richened. If there is a lower pressure in the intake/carb bore, more fuel will be drawn in, not less. However if there is a downstream air leak more air will also be sucked through it, effectivly worsening the air leak.
Now if someone with a plugged filter leans the carb to get it running as best possible or to full factory RPM it could be too lean in the cut or after setting the carb with a plugged carb someone then cleans the filter it would end up too lean.
Lots of filters tend to do a better job filtering out crap once they get plugged up a bit.
if you use dyno premix and it is running too rich because of a plugged Air filter and a saw that is very dirty IE, flywheel fins cylinder fins and top cylinder cover,,,and it gets hot,,,, and you keep running it,,,,,and you are compressing dead dinosours,,,,,,guess what you get,,,, stuck like chuck,,, almost looks like diamonds and an overly rich, overheated stuck piston is He_ _ to get unstuck!!!!!!!!!!!!
too rich can also be a problem!!!!!!!