I don't have a generator but do keep my bike in the garage, perhaps a small computer fan in the garage door to keep a negative pressure in the garage would solve any odours entering the living area.
Possibly, i used my experience with the generator to show what happened with the petrol fumes even with the filler cap in the off position which is supposedly sealed.
I kept it like new and it was spotless so it wasn`t like the dirty old oily smelly ones you see.
When the genny was outside we never noticed the petrol fumes when switched off even when sat quite close to it however ........................
Once it was inside with both garage doors shut we could smell the petrol within a minute or so even at the front of the motorhome where the seating / lounge is.
Can you possibly put the bike in a confined space for a while then open the doors and you might smell what i`m trying to explain.