Are you sure that the thin layer of grease can catch all the particles that pass the cloth modification you have instead of the original filter?
I change the filter about every 5000 and the inside is always clean.
Air filters are cheap, around 10US$ for HiFlo or RMS that fits on my scoot.
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Yup - in this case (Agility 125 air box) I'm 99.999 % sure.
Like the previous inspection, I completely removed the modified filter for proper inspection. Both times the filter mesh was perfectly clean. I also had a good look at the inside of the pipe between the air filter box and the carburetor. If any dust passed the filter mesh, I should at least find signs of dust at the inside of that pipe. I did not found signs of any dust.
I think the shape and separate "compartments" of the Agility's air box helps to get the dust trapped in grease.
I actually started smearing grease at all my vehicles' air boxes a number of years ago. Depending on the shape of the different air boxes, more (or less) dust always get trapped in the layers of grease.
In my previous bike's case (Honda NC700X) not all dirt get trapped in the grease - simply due to the shape of the box, and the location of the air intake pipe at the box.
Just by smearing a thin layer of grease at the inlet pipe to any given air box, normally helps to collect a lot of dirt that enters the pipe.
I know the OEM filters are cheap, but in my case our dealers seemed to have disappeared. Apart from that, I dust decided to do this trick on the scooter as well. Simply because I already knew the "grease trick" always works well.