scubabunny

Please help me. I got a bad tank of gas. Took it for repair. Got a new fuel filter, spark plugs and cleaned the carb. Now the bike will only start with the choke on. I ran it for 5 minutes, turned the choke off and the bike off. Tried to start it with no choke and it will not start. Also, when I start with the choke on, when I turn the choke off, the bike dies. Before all this......It would really backfire upon downshifting and holding the clutch in. Someone had put Vance and Hines pipes on it before I bought it from the used bike dealer. What do you think it going on?? 2007 Yamaha with 4200 miles.