Thanks Threadbear for that, [who are you by the way?] you seem to have thought it through more than others. I remember the good old days when I ran my Ariel Arrow on SAE 30. Never gave any problems but would stink something awfull! I had a word with Andy Woolley earlier and he uses 40:1 with mineral oil. I have a steel conrod and needle rollers so I think I'm ok with synthetic and I always use a know brand primarily silkolene. All my oil seals are good and the carb is well tuned. You may have hit on it when you mentioned oil settling during periods of none use, as I remember the smoking was last year early spring when it came out of hibernation. It eased off with subsequent refueling. I dont use an in line filter because they are nothing but trouble and I dont need a magnet as I sealed the tank with flowliner some years ago.[I have used it in all my cars and bikes, great stuff, I recommend it!] It was interesting what you found out about the nature of the oils, part carrier and part lubricant, I guess most synthetic oils are designed for autolube systems. Well, I have decide that this year I'm sticking to synthetic and will try 35:1. Interestingly my little Tomos moped [the only moped to be sold by Woolworths!] uses a 50:1 mix, now that is lean!