Not trying to sound disrespectful but I am very experienced with these little engines as I have owned and killed 3 engines over six years while constantly researching more about how they work and doing experiments.
I always keep my air filter clean and use a fuel filter. I use a very thin brass wire mesh from a wok/fryer strainer from a junk shop. Behind that is a proper brushcutter foam element which I regularly.
As for oils I have tried many of them. Valvoline seems best for break in while running rich as allows wear in and has the highest burn rate of all the oils I have tried while still providing protection. Bel ray seemed to run dry and hot, Castrol seemed fine, cheapies seemed to degrade and leave residue. Eventually I settled on Motul 800t, specifically designed for premix and full synthetic I mix it at 35:1 and more and it leaves too much gunk on the piston head. The only drawback apart from cost is that the Motul does build up residue quickly on the head and in the muffler however this is easily wiped clean and absolutely no deposits are left on the rings.
There is a new high performance and even higher burn rate Valvoline oil I saw I may use this with the Bi-tron as it has made my expensive Motul redundant.
I'll just say again that in all my years of experimenting This stuff has given me by far the best improvement and it just keeps on smoothing out with every tank I use (now six I think) My 6 month old engine now feels as loose as my old one after nearly two years!! By that time the compression has dropped due to wear. Right now I have a loose-y-goose engine with poppy compression and power galore. It never has trouble starting NEVER need the choke and never overheats even on a hot day up slow hills. It never feels angry and dry after long runs on hot days never feels like it going to pop when revved out. Like I said it feels like a second break in and I am thoroughly impressed.
I decided to use more of the fuel conditioner with the last 5L can which has the very thin grade polarized treated oil the idea was that it would better penetrate the nooks and cranny's of the engine, this seemed to accelerate the smoothing process but I can't really tell for sure.
I am still waiting for equilibrium... How loose can it get without melting off the bike into a puddle of lubricated gooooooo!