ORIGINAL: pe reivers
Thanks! We just beat France 4 - 1!!
As you may already know, I am not a believer of lean oil mixes, and your observations confirm my findings.
Richer oil mixes are much less critical. The increased viscosity of the fuel "seemingly" needs richer fuel settings, because the needle is opened more to allow for the same fuel flow.
It's not the viscosity that is so much the issue... it's the amount combustible material in each unit of fuel.
With 20% oil you have 8% less available methanol per volume unit of liquid that passes through your carburetor so consequently you have to richen the mixture by a corresponding amount.
You are correct that the needles will be a little more sensitive with low-oil ratios but this should not be excessively so.
We run 5% nitro in our 2-strokes and 10% in our 4-strokes. With this small amount of nitro, perhaps our needles are a little less sensitive than when on a 0% nitro blend.
As for the power-gain/loss.
I picked up 600rpms in mid-winter when switching from 20% Morgans castor/synth blend (same stuff as in Omega) to 12% Coopers Plus-C.
I put this down to the improved lubrication qualities of Coopers and the lower viscosity (especially in winter).
The effect is not so pronounced in mid-summer but still measurable.