Do not buy a 125 4 stroke. You will hate it before a week. Even my race tuned 125 wr Husky is horrible to ride on the road and just has enough power for a decent off road session.
I have ridden 125 4 strokes and you'd go faster and have more fun on your bike. If you something fast and fun get a Husky, if you want it to work all the time buy a Yamaha or Honda but it won't be half as fun when it's working.
I seriously recommend a 250 2 stroke, the are cheap and easy to fix and so much fun off road.