I have a bunch of jets and some are stamped on the bottom, some on the side.
I've been having issues with mine too, and just throwing in a new pilot jet helped a lot. I cleaned the old one out, and could see through it, but not as well as i could see through the fresh one.
Good luck!
Also, if you're on a budget and the bike is not holding compression, and if you can afford a top end gasket kit and some rings, you could just throw new rings on there if the piston and cylinder aren't bad. Rings usually wear out before the actual piston/cylinder do. Have the cylinder honed though, which just makes new scratches for the rings to seat with. A local dealership honed my cylinder for 5 bucks. Rings were like 30 (damn factory yamaha parts!!) and I got a gasket kit for probably 30 as well.