Jokes are best delivered on April the first.
Get rid of the modifications and additives, put it back to standard and ride it.
Every change you list has put the engine at risk and you clearly have less idea of how to run an vehicle than the idiots that sold you the "marvel oil". If you talk to the guy that sold you the marvel oil he can probably convince you it works as an enema as well and you can blow white smoke just like your scooter.
As for the white smoke, you did it you figure it out, its most likely your scooter asking the rest of the world to save it from your foolishness.
Why would you remove the aircleaner? Why not just throw some sand in the oil filler and save the effort of riding the scooter around to stuff the engine.
As for the hard starting, why would it want to take any more of your abuse its probably scooter artificial inteligence survival instinct.
If you want more performance buy a bigger scooter, if you want a clapped out scooter go to a wrecker and buy one prepared for you.
The only reason I write this is so the dealers and mechanics out there that read you post know someone else understands.
2001 Yamaha Zuma, DR Evo 68 cylinder, Leo Vince TT derestricted, Delorto 17.5 (#98 jet), standard aircleaner, RMS fan, Race CDI, Standard oiler and premix @ 75:1 Shell SX2, Doppler SR3 variator, RMS clutch, RMS R rear shock absorber and Pirelli SL26 tyres.