I would say your rings and piston are not the right size ?..and your burning a lot of oil !!..lol. and from the looks of that last pic of the piston in the cylinder..it looks to me the piston has too much clearance between the piston and cylinder wall !. did you do a compression test before you tore it down ?..if so..what was the reading ??.
I doubt it ??..again..any time a ( atv in this case )..spits fuel out the intake..or shall I say carb ?..this tells me it's out of time ?..or you have a bent valve ?..and not enough compression for the motor it cycle on it's own !. here's what I would do before I tore it down ( which you already have done now..lol ). I would have did a compression test...and see where that stood ?..if it was low ???..then I would lean more towards a bad piston and rings ?..bent or broken valve ?.orrr..as I have already mentioned...a bad cam chain !..and these models are really bad about the slack adjusters going out in them !. sooooooo..after I got the top end down ?..and seen that everything was ok ?..then I would focus on the carb...and cam chain. I just completed a 1998 trx400 4x4 today, it needed a new piston and rings, carb gone through. was fighting this thing for about a week waiting on the cylinder to be bored over..and the new piston and rings to come in. well..while I was waiting on those parts..i also pull the slack adjuster off the top of the case. I knew right away..when I pulled both bolts out..and the slack adjuster just sat there ??..I knew for sure the cam chain was history !!..soooooo..now I jack the front of the atv up as far as my floor jack would go..and started unbolting the front engine case..yessssss..I did loose alittle fresh oil !..lol..but I can deal with that. as soon as I got the case off..i looked inside at the cam chain and cam sprocket..sure as i'm sitting here typping these words...the punch marks were about 6 links out past the timing mark on the inside, top side of the engine case !!. this bro..is a dead give away to a motor waiting to explode !..lol. soooo..now you have the basic idea on what I would be doing to your machine if it was here in my shop !.Maybe a dumb question, but could the carb float just be stuck?
not gonna fly as I told you on the phone..lol. that ring is wayyyyyyy bad/ worn..maybe not the right ring to begin with ???..who knows !..lol..I know this..i would never sell a atv to anyone with a bad top end job like that !..lol. take the cylinder..piston..rings to a machine shop that works on atvs..motor cycles..anyone that can bore it for you ?.and tell them or ask them...what all you need to make that motor run as far as the top end goes. oh..and I seen the head gasket..looks like it tore some ?..I would go ahead and replace all the top end gaskets just to be safe !..lol.
click the browse button after you upload a pic..then when it's loaded..click the browse button again..it should take you right back to the pic files that you just got done up loading from..then click on another pic from that file..then hit the upload button.it should attach it with the first..you can upload up to 5 pics at once per thread post.