Indeed ..... Surely it can't be that long, till they can make a piston with a surface so msooth, it just slides against the cylinder bore with no need of any additional lubricant ....That makes sense; if there is not enough oxygen for all the fuel to react completely with, then not only will I not have liberated all the Joules I paid for (which is bad enough), but there will be carbon present among the combustion products (soot you, sir!). And having electrically-conductive material around the spark plug gap probably isn't going to do the ignition any favours.Yeah ..... 50:1 versus 40:1 is 20 ml. of oil versus 25 ml. per litre of fuel, which is a difference of 25% and therefore potentially significant. So I think I'll just carry on mixing up just as much as I need each time; but it doesn't sound as though a small amount of 40:1 added to a larger amount of 50:1 would upset anything too much, so if I make up too much for the chainsaw or strimmer, I needn't worry about dumping any excess into the genny tank. 1 litre 50:1 plus 100ml. 40:1 = 20ml. oil + 980ml. petrol + 2.5ml. oil + 97.5ml. petrol = 22.5ml. oil + 1077.5ml. petrol = 1.1l of (1100 / 22.5):1 = 48.89:1, which is well within the accuracy of the provided measuring cup anyway.
Good to know that the theory translates into practice!