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Airhead
pdlouche
I think the logic is on the lines of the amount of oxygen available is limited by the swept volume of the cylinder(s), and an excess of fuel leads to incomplete combustion and carbon / unburned fuel in the exhaust part of the cycle with soot deposits around the cylinder head and exhaust. Petrol has a calorific value significantly greater than lubricating oil, so reducing the oil increases the proportion of combustible fuel in each cycle, i.e. increases the proportion of fuel that cannot be burned. Because the oil burns less readily than petrol, the unburned portion tends to be mostly oil, giving an impression of too much oil in the mix.
I can believe this applies to older engines where everything goes through the carburettor and oil levels are much higher (the handbook says 20:1 for my 1952 Trojan!), but it might be different for newer designs where oil delivery is separate from petrol?
In any case, you'll often find complete strangers will claim to know more about your machine than you do, especially if you can't get it going and a crowd gathers...