I also run my chainsaw 25:1 even though Victa say 50:1 with their oil (I am using penrite synthetic so it is even better than their oil JASO rating wise). Personally, I believe all this 'can run at 50:1 with our special synthetic oil' is balderdash.
If its not fouling plugs or making smoke clouds after 35 years of use on 25:1, then the extra oil probably isn't making enough carbon in the ports and under the rings to worry about. Probably a sign of a high quality engine that it can handle the bit of extra oil.
I have to keep 40:1 due to my McCulloch leaf blowers condensing oil severely out of the muffler if run on 25:1. But I really don't hesitate to use 25:1 in any of the Ozitos, MTD or GMC that want either 40:1, 35:1, 32:1 or 30:1
