Bike guys, help.

AlV said
Couple of places online have the petcocks for your bike. Looks like $25 bucks gets it done.

http://www.partsnmore.com/parts/yamaha/dt125/

Good luck
AlV

And worth every penny.
Those are good bikes and I'll bet that one scoots.
I used to have a DT360 when I was young and stupid. (never hurt myself on it though) :-)
I have an XR500 Honda now. (old and stupid?)