I stopped by the local shop today to grab some oil and the only yamalube they had was the semi-synthetic 20w50. Mechanic said that that was all they use when doing oil changes (ironically, the place used to be a combined yamaha/honda dealer but yamaha just moved out a few months ago and they still use yamalube) Anyhow - my dad told me not to use any synthetic oil in my bike ('77 xs400d) but he rides a Victory and doesnt work on it himself so he knows nothing. When I got back home I noticed on the bottle that it said it was formulated especially for v-twins (like how in the hell is the oil supposed to know if its in a V or parallel or inline?). Is there any reason I shouldnt use this stuff? Tell me now, otherwise I'm dumping in 2000cc's of the "semi-syn" tomorrow and giving her a good flogging around the city. Thank God it finally warmed up a little.

Semi should be fine but I would avoid fully synthetic on a bike of that age.

Its cause the clutch runs in the oil, that full synth causes slipperage.

semi synth is still mineral based but with additives which stabilize and clean the engine. I use Millars 20w 50 in my xs400 and costs £30 for 5 litres but I think that is money well spent. Just stripped down my engine to change cases and its purfect inside!!