Yoshi's are fully packed design with a straight through baffle.
They also have an optional sound level reduction insert that fits in from the end into the straight through baffle.
The packing of the cans degenerates over time, this is not a maybe, the packing only has a certain useful life.
The exhaust gets louder and the shell temperature gets hotter, especially at sustained high power levels or many hours of riding.
You can buy repacking kits from Yoshi that have new bands and rivets, or just buy aftermarket packing, reuse your bands, and find suitable rivets.
I have Yoshi's and when the packing is in good shape they are one of the quietest cans one can buy.
I had exhaust stink with the stock cans and still have it with the Yoshi cans, but nothing as bad as you are describing.
You can't get rid of it, as the exhaust outlets feed a low pressure zone behind you or your passenger and that keeps the gases from jetting away.
Try regular gasoline if you are using premium, as depending on the respective formulations it may help.
Some have found improvement by using a Power Commander to permit fuel mapping changes.
The exhaust issue can be bad in stop and go traffic.
The best solution is putting on a low can 4:1, as many here have done.
Most have been 900RR adaptations, but there are aftermarket 4:1s with low mount can that you can get either used or new.