I Need Help Baddly

hi i have a yamaha 100 enduro bike and i rode it when i got it it sat for a couple weeks then i tried to start it the compression seems low the kick start doesnt go back up all the way,when i get it started i have to put gas straight into the cylinder and when it starts it revs way too high and it will only stay running for about 5 seconds
if u can please help me