got a little smoke
 

Yardsport (american sportworks) YS200 with the GY6 150.Its starting to use a little oil. Well maybe more than a little just started tracking oil use. I have not done a compression test yet. Is it time for the big bore upgrade or keep it stock? It has enough power for my needs but more is always better right? Looks like several variations in the cylinder so how do you choose? I hope I can wait until the season is over so repair can be a winter project. FYI I use this thing for running the dogs and having a cold beverage every day so it sees 5+ miles every day.

It sounds like your rings are worn out. If your going to rebuild it then i would say go ahead and jump to the 155CC 58.5 mm kit. Its a drop in kit just make sure you measure your stud spacing to get the right one. Its the least amount of work and i did notice a difference in mine when i made the change.
There are other kits out there but there is alot of contradicting information.
Some bigger kits claim to be drop ins but there have been complaints about how long they last. At 1 time i saw a few posts that said it was easy to bore the case with a dremmel or rotor tool to fit the 61mm cylinders but haven't seen one of those in a while and the general consensus i have seen now recommends getting your case bored by one of the supporting vendors to ensure quality and accuracy.
If you decide to stay stock get the complete kit Cylinder, piston head and rings the cost is not very expensive and better to be safe than sorry