even if it looks good, most likely there is some excessive wear in the bore. unfortunately most all aluminum bores do. if you cant precision measure it try a new ring to check the end gap. compare it to factory specs and itll give you a good idea, check it in different areas of the bore, you will find some taper, with the lower part of the bore almost perfect and opening up towards the top. check the valves/ guides for wear and check the breather to see if its working properly, if it is smoking really bad it may be more than the piston/ cylinder causing it. if you can get ahold of one, do a leakdown check.
if you go as far as a rebore, they wear so fast its frustrating. I have tried different grit on the final hone operation. wear rate doesn't change, its just the fact that the aluminum is not optimal for a cylinder.....