It's hard to explain since I don't know what it is or have a picture.. But it has the needle inside of it and a spring on top I believe..It has this notch that has to line up with something in the carburetor.. If you don't understand my terrible explaination it's alright.
You should really download this (or all that apply to you) manual. With the manual and parts manual you should never have this problem again (not knowing what its called). Plus they will tell you and show you how everything should go back together. Doesn't hurt to read a few pages every time you get a few extra mins.. With these machines, knowledge is key! I:I http://www.blasterforum.com/general-support-17/downloadable-yamaha-blaster-manual-17325/