I picked up some Stihl synthetic after reading this.
I also found a seller of straight gas, but closed at the weekend. I think ethanol may have caused my Subaru Robin to run badly, added Seafoam. Now much better.
I noticed on the UK board that they have access to a product called Aspen, I have a a feeling that a lot of issues can be put down to stale fuel.
This is one of the reasons I've switched to AV gas for all of my yard equipment the past couple years. I haven't had an issue with equipment working in the spring and having to rebuild carburetors since I have. One of the other great things about AV Gas is how it evaporates and doesn't leave a obvious residue which I love. AV gas is required to be "shelf stable" for up to two years because they use it in remote fuel dumps in places like Alaska.