Could be a couple of things. First do a compression check on both the cylinders you should be above 125psi. Some times if the motor is started and shut off a bunch of times without letting it warm up to temp that kind of thing happens also.
You might want to check the bolts that attach the y-pipe to the cylinders and the doughnut between the y-pipe and exhaust pipe. With the issues that were mentioned in the other replies this is where the oil/fuel will leak out and make a mess. Once it is warmed up and ridden it should burn most of this off but there will still be some residue.