A few weeks ago I discovered a canister of gas, about half a year old from another project. I did notice it smelled a bit weird, but the smell didn't register enough to keep me from topping off the tank with it.
After that, I had business about 550km away and thought it a perfect opportunity to take a ride. After not even 100km, the motor started stuttering, warning lights flashed and then it cut off completely. There was a gas station close by, so I stuttered my way over and filled up again. The whole trip took way longer than planned, because the motor would start stuttering again after less than half a tank and I would have to fill up again.
Arriving, the motor would die under 2000rpm, so I had to keep it at least at 4000. The backfiring didn't help my mood much either.
On the way back, the bike was much better behaved, and I hoped that it finally burned through all the bad gas. Relief! Thought I'd treat it with some additive to hopefully clean out the fuel system. But then the stuttering came back - so bad it was obvious the only trip for me would be to the dealer.
So now I'm anxious to see how high the price for my stupidity will be. And I swear in future my bike will only get the best super plus!
Additives are generally snake oil, unless you know exactly what condition you're trying to address.
Also additives often don't combust well themselves, adding to the issue.
I suspect the old gas had 2 issues: it had already lost some octane because gas is volatile - it will slowly evaporate the most volatile compounds first.
Plus sitting gas attracts water out of the air.
What you describe is much like what happens when you get some water in the gas - these intermittent sputterings when a little of that water gets to the combustion chamber.
About the only additive I'd use in this case (that is, thinking there's a bit of water contamination) would be some form of alcohol. It has the ability to bind with both gas and water, so instead of a blob of water getting injected (or pulled through the carb), a tiny amount of water gets combusted with a lot of gas on every cycle. "Heet" is a common brand in the US.
Any kind of very high proof alcohol will work (90%/180 proof) - higher is better, as the remainder in the alcohol (that 10%) is water.