I have no idea where the word is coming from or what its word stem is. The meaning of voll Karacho is something is going with a high velocity or full force. Unfortunately, this great word seems to fade away.
When I was a child, we used “Na der is owa voi Karacho g’fohrn” for every vehicle that went just above walking speed. It was very nice to see this word on a playground. Thank you, Munich! You made my day.
Homework: Tell somebody about a fond childhood memory.