This is a story from my Honda 250cc four-stroke engine.
After of several months of good operation, it came one day that the engine has major difficulty to start up, especially when it was unused for a few hours.
I am using a specific refuel station, so to be in control of fuel origin.
My Honda has only electrical starter, and all Honda's are famous about problem free engine starting.
Either way I did start to investigate the symptoms, occasional spark-plug misfire with cold engine, after engine warmup the fuel was burned as usual.
Two years ago with the same symptoms, I was had to throw away all gasoline stored at the fuel tank, along carburetor, and to leave the entire fuel line to dry.
Then refuel with clean fuel, and everything started working as usual.
This time I did stored in glass bottles, all the removed gasoline 1.5L , so to try to inspect it.
There was not any water bubbles visible (separated water), instead the entire fuel seemed having powerless odor, and it did not even evaporate as fast, as it does gasoline at perfect condition.
And therefore I came down to the conclusion, that for a second time, water accumulation within the fuel this became my problem to solve.
The solution
This is two simple advice's:
1) Never ever think reusing fuel which were removed as contaminated.
They are plenty of justifications out there, scientific and not scientific, about water accumulation within the fuel.
But there is no fuel detector device ( a tester) so us to use and be aware of actual fuel condition.
2) There is no gasoline filter this able to stop water this from moving within the fuel line.
Greece this is not famous for rainy weather and long winters, even so lesson learned, once a year I should dry-up the entire fuel line, along the entire fuel tank.