i bought a 1987 tw200 yesterday, got it home and rode it around for about 10 minutes or so. After 10 minutes the damn thing started to backfire on me so i rode it home and it died as i pulled in the clutch in the driveway. i should say first that it wouldnt stay running without the choke on, so i rode it around with the choke on. i got home and inspected everything. the gas tank was pretty rusty, so i cleaned that out. i cleaned the carb and nothing was clogged up. but, as i was sitting scratching my head i discovered a missing screw that i suspect vibrated out when i was riding which is when it began to backfire. its number 30 and 31 in the picture. i have no ideaq what it is or what it is for. any help would be awesome!