I have used petroil on my racing and road Scotts for many years. I use the cross over system with one way valves. This ensures that the mains are lubed. I use 25 to 1 mix with Silkolene Comp 2 or decent equivalent. The semi-sythetics seem OK for most uses, but I do like R40.
I have run std oils at 20:1 but they seem to be marginal and this ratio is very smokey. Running a good oil at 32:1 is probably OK for the road, but oil is cheap compared to engine rebuilds!
I fill in the crankcase oil resevoirs , not to increase the primary compression ratio(which I prefer to lower from standard) but to reduce smoking on start up or after long periods in traffic.This works well.
John Farrar
