In normal use it is recommended to go at 20:1 unless you use the manufactuers genuine lube!!. Then it can be alot less. I have used synthetic 2T lubricants for over 25 years and run all at 33:1 irrespective of what is said. I now have a McCulloch 310 Saw with over 1000 hard hours of work in 25 yrs and the bore is perfect. I have no doubt that is due to being maintained.
Back to your question, it's up to you to decide which to use. If in doubt go 20:1.
Peter., April 2007
My McCulloch is a 10-1 mix, not sure of the model though.
