Ok this arvo I cleaned and lubed the chain, and topped off the oil in my GPX250. It looked a little low. I then went to Hurstville and back from Maroubra. Around 40 minutes of riding... thought that the bike sounded strange, like a rattling of some sort... But thought nothing of it. Turned off Botany Rd on Wentworth avenue (not the one in the city) and it happened. The bike made a 'swallowing' sound, and the engine sounded like it was 'muffled', it's hard to explain. I pulled over, and it died whilst slowing down. Started it again, and kept the rev high because it would die on idle, and A LOT of smoke was coming out of the left exhaust (GPX250 has 2 exhausts). The smoke did not stop and luckily made it home, but it still has the same problems as of now. It will not go above 60 KM/H no matter how much I pushed it, and has a lot of trouble going from 0-60. The sound is very hard to explain. Before it sounded clear, and kind of high pitched. Now it sounds like a low grumble, like it's muffled or covered. I think it may be the oil but I need the bike to be running for tomorrow as it's the only mode of transport I got, please help!