There's a big difference between a gasoline odor from overfilling and an exhaust odor. If the odor is exhaust fumes, I'd suspect bad exhaust gaskets. Several folks have had to have them replaced well before the standard maintenance interval, and BRP redesigned them. Another possibility is the addition of a larger windshield, which can sometimes cause exhaust fumes to accumulate or be drawn forward.
If you did overfill and the evap canister is full of gas, it will take a long while to dissipate.
-Scotty