Bit of back-story here: Dealer used 10W-40 semi-synthetic oil in his
scooter. Manual advises 10W-30. Owner contacted HONDA,UK.
I find what HONDA has to say about semi-synthetic oil being preferable for "motorcycle engines" , rather than fully synthetic, to be quite interesting~!
Sure - no one reports a blown engine while using fully synthetic oil......for zillions of miles and in dozens of powerful what-evers.
But if semi-synthetic is better, for any reason, why not use it?- I'm thinking.It's probably also less expensive.
Stig