That's just a reality of low ELO, or really anything other then high ELO premade 5s. Seeing as I'm 750 ELO, I obviously haven't figured out how to carry a losing team either, even when I'm personally doing well, which is probably less often then for you.
However, my best suggestion would be to find a lane that's doing well and get them fed, especially as the jungler. Abandon the feeding lane, because eventually they're going to stop being worth so much gold to whoever's killing them, and if you do try to gank for a lane that's far behind, you'll often end up giving up a double kill or worse. Once towers fall, be ready to protect the weak lanes while they free farm, and punish anyone who comes after them too deep. This is alot safer then a gank between the outer towers, and you'll often be able to coordinate with other teammates by this point.
Try to control objectives, and punish anyone who's out of position(provided you can be sure they're not baiting). Do what you can to disengage dangerous teamfights, and engage advantageous ones, and if you win one, immediately capitalize with a dragon, baron, turret, or inhibitor, depending on the stage of the game, what's most available, and what's most worthwhile at the time.
Above all, do NOT criticize your weaker lanes. Rather, encourage them, and try to keep your team chemistry together. If you lose that, you will lose the game.