With my last couple of bikes, both CB500s, which I've put a total of 160k miles on, I mostly used super unleaded because they seemed to run slightly smoother and have better fuel efficiency with it. With the Firestorm, I tried super unleaded early on and found absolutely no difference, so have been using regular unleaded in it. However, the other day I filled it with super unleaded and found that the above symptoms are totally gone with it. It's definitely got more go – not more torque per se but crisper throttle response and better running on WOT at lower revs – and the 4k rpm stumble has gone.
While I know that these engines certainly do not need 97 RON petrol and will not make more power with it either, is it possible that the ethanol in regular unleaded (I understand that there's less of it or maybe none in super unleaded) is causing these symptoms? I know these bikes are sensitive to fuelling changes so I'm wondering whether the ethanol content affects this and hence causes the above symptoms?
It's absolutely not a placebo effect – I ride my bike every day or nearly every day, have put 50,000 miles on it since I got it in June 2016 so know it quite well, and am pretty sensitive to things changing!
I'd rather not spend £18 instead of £15 every time I fill it up, but if it runs better then I'll have no choice
![Very Happy :D](./images/smilies/icon_biggrin.gif)