Everyone,
The following list is probably missing something but there are at least nine factors that determine how well an engine runs: degrees at full advance, rate of advance, mJoules in the spark, shunt resistance of the plug, combustion chamber shape, compression ratio, inlet tract geometry, chemical composition of the fuel, and octane rating.
Although some of these variables are fixed when comparing two otherwise mechanically-identical engines (e.g. two Comets), even then there are enough "variable variables" left to make it very difficult to arrive at definite conclusions. That's why I asked if anyone is aware of something published by the SAE where experiments were conducted with enough of the variables controlled that conclusions can be drawn about what, if anything, we need to adjust to compensate for modern fuel.
The latest Forum update seems to have made it impossible to quote the relevant snippets of text when composing replies off line, which is a step backwards in my view. Be that as it may, Albervin wrote "The other additive I bought is a fuel stabiliser. It supposedly stops our modern excuse for petrol from going stale and is quite cheap compared to the octane booster, about $2.50 for a 236ml bottle. Ideal for when you don’t use the car very often."
I did a year-long "scientific" study of a popular brand of stabilizer back in the '00s. Making a long story short, I estimated the total area in a Monobloc's bowl for fuel vapor to escape from it, then made containers with holes of that size. One container held gasoline from the pump, and another held the same gasoline plus the highest recommended dose of stabilizer. The initial volume of both containers decreased rapidly at first as the most volatile compounds evaporated (which is why your bike is hard to start after sitting for a few weeks -- assuming the pilot jet didn't get blocked, which is another likely problem), then continuously slowed. I'd have to look up the data to be precise, but at the end of something like a year there was only a tiny amount of tar-like residue remaining in each. I used a precision scale for this experiment and found that the fuel stabilizer made no difference whatever in either the rate of evaporation, or the quantity of residue left after a year.
For what it's worth, if I'm not going to ride a bike for more than a week I drain the carburetor. My main reason for this is I've found within a couple of weeks a thin membrane of "varnish" forms to block the pilot jet, which makes starting a lot more difficult than if only some of the volatiles are missing from the fuel in the float bowl.