1980 Suzuki 550L Engine starts, runs a few seconds, hen stops.

take off complete cover

Looks like your key needs to. Be coded by a Suzuki dealer

my mechanic told me the same thing and I've been using castrol straight 30 wieght oil for years and i own a 1989 kawasaki ninja 1000.

carbs need to be cleaned and set

Most bikes before 1980 have points (i'm sorry but I don't know for sure with yours, ) however if you know, then ,,, check the points and everything connected to them, if your sure that the coil has power, then its going to be a problem in the car , ie rotor , points, or the cap itself

remove the cover behind the shift lever, remove old cable and fitting that runs into top of said cover. Next, route new cable from lever along handle bar, run under gas tank and then between the first and second carborators poke cable through hole at the cover,thread in fitting,attach to spring actuater adjust as needed,

Check the mouting locations and carb boot/seals for cracks. this appears to be a vaccum leak nad the previous area's mentioned should be checked as well as throttle position.

the jetting/ jets are fittings inside of the carburators that allow onlky a certian amount of fuel to burn so the motorcycle does not flood itself out by having to much or to little fuel

Make sure you have a fully charged good battery and clean connections.

u need new needel and seats in the carbs . u can check the old ones with a vaccum gauge the should hold pressure at about 5 psi