According to my long-term experience on BMW as a mechanic, about Ks specifically: the less ethanol there is, the better it is.
So no ethanol is ideal, E5 is OK, problems start with E10.
These problems are:
- fuel pump damper desintegration: ethanol melts it.
- fuel lines desintegration: the same. Inside fuel lines create unsolvable leaks as you can't see it inside the gas. Outside fuel lines will burn your bike.
- fuel pump death: by absorbing water when stocked a few months, ethanol creates a gel that sinks at the bottom of the tank. This gel is then sucked by the pump but it can't deal with its resistance and dies. The fuel filter is also concerned and will be clogged.
- I also strongly suspect ethanol to alter the fuel indicator seal.
- As the tank is in aluminium, corrosion seems not to be a concern. But the fuel tank cap suffers from it.
The less, the best...
BTW , do you know why we have this ethanol in the fuel?
No, it's not to save the planet or polar bears.
In 2017, European Union stopped the sugar production quotas, at the time the price of sugar was very high.
As predicted by economists, every producer invested to raise their production (mostly from beets)...but buyers did not put 10 sugars in their coffee. Same demand for over production : the price of the sugar collapsed and thousands of tons of beets were let rotten in the field.
The solution to use this excess of sugar was to transform it to ethanol and to create a regulation for a mandatory part of ethanol into the fuel.
Paint it green, lower taxes, it will sell.
Damage to fuel tanks is not the worst, after all. Beet culture relies on a large pesticids use , that decimates insects, particularly bees ... Beet lobby is so powerful here, it managed to derogate to neo-nicotinoids prohibition.