well... the "mechanics" you talked to aren't worth the dirt under their fingernails
A paper coffee filter is way too weak and tearable... not to mention that if it gets wet they are even weaker.
(bits of paper can and will get sucked into the motor)
They are also wrong the 2 strokes are somehow tougher than 4 strokes... thats pure nonsense.
I have heard that auto parts stores sell a foam air filter material that you can cut and fit for your situation... (maybe even glue together with hot glue or something?)
You might try that.
The important thing is you do a plug chop with a fairly new spark plug to see if you are too lean... if it is... you are risking a seized (destroyed) top end on your motor... (piston and rings and bore) ... you do NOT want that to happen.
Thats about $100 to fix.
I have an FA50 and am working on it now... I will have some better info after a few days... (I haven't looked at my air filter yet.)
Be careful with those paper filters on there.