Have just spent a couple of weeks struggling with 2 strimmers and a chainsaw that wouldn't start or run properly. Discovered pretty much by accident that the petrol bought from Alas in Perello was the problem. Tried Repsol petrol from the next garage and all is well. Used the same oil in both mixes and even went baqck to try the Alas juice again and the problem re-appeared. Alas petrol is blueish in colour and the Repsol is orange-ish. Another chainsaw and a little 2 stroke generator seem to run fine on either.
Might solve someone else's problem.