The father of a couple of friends of mine had a Bultaco just like that, back in the day. Joe, who was my age, rode a Sachs in the local MX races, and Lee, his older brother,(and later my sister's boyfriend) rode a Bultaco 125 flat-track bike. I rode the flat-tracker once. It had been heavily massaged; radical porting, stuffed crank etc. Lee warned me to keep the rpms up, or it would load up. Sure enough, it got loaded up, and then it suddenly cleaned out, and pulled the front wheel straight up! That bike had a wicked power band!