Converse, I repaired a mates mower last year (talon) and he asked why it didn't smell as much during use. All I had done was drain the dirt out of the tank & carby and refill with fresh 98 octane. Maybe 91 has more sulphur in it and make it stink. Fuel and can was fine - it was the fuel line disintegrating inside that made it clog and surge.He said it returned to normal smell after he refilled.
That being said, when ever I really hammer the car (which I try to avoid but sometimes you can't), it stinks of rotten egg gas from the cat convertor, and thats on 98.
I am in the process of reading a rather interesting book on motor petroleum, and it does make mention of a quite concerning increase in octane requirement with even small amounts of carbon build up. Once I have a bit of a re-read, I will remember what the figure was. Its is a book made after tetra-ethyl lead, but before MTBE was banned
