hello guys im new here i bought a 96 honda ex300 since about a week
i still dont know about the ATV that much but i understand in mechanism
so the thing is i bought used honda ex300 with a new motor
so what i did tried to maintain it but checking oil,air filter etc…
i noticed that the ATV is low on oil so i went and bought thick 10w40 semi synthetic
added some and fueled it up with 98 octane
so i started to notice white smoke on high revs
either way the ATV runs perfect it goes fast and engine sound is great
however that one thing the white smoke that comes out
i called and asked the guy that i bought the ATV from and asked him if the piston rings are good or they need to be changes he told me everything is new in the motor probably because u mixed semi synthetic oil with synthetic oil

so i appreciate if someone could help me find out what is the exact issue here
or piston rings or fuel or oil