You didn't say what year so. You unbolt the rotor and remove the rotor, unbolt the timing plate and take it out, then you should see the advance mech., I can't remeber how to remove it. Make sure you bolt down the rotor before you try to start it, you'll be hitting you head against the wall trying to found out whats wrong with it, if you don't bolt it down it'll jump off and it won't start.
EDIT: I now remeber how I removed mine. It's slides off the camshaft. My didn't want to slide off so I had to get a screwdriver and wedge it between the head and base plate and the wiggle that thing off.
1979 Honda 110 ATC, CEET gas tank cover, 25X11X9 rear tires
1984 Honda 110 ATC, orignal blue plastics,
1982 Yamaha 175 TRI-MOTO, 26MM Mikuni
Honda US90 ATC, Collecting Dust
2004 TRX450R