My Honda 125 uses 10w 40 semi synthetic oil and I was wondering if it would be ok to use 5w40 fully synthetic as I have quite a lot going spare. ;-)

Some older clutches don't like fully synth.

[Edited on 29/9/20 by big_wasa]

Its an automatic

Are you sure 5w 40 isn't already on the list of oils? all the engines I've seen bike & car allow a large range of oil viscosity mostly depending on the climate. And yeah your 125 isn't really a pushing it race engine, would probably be happy on old chip fat

I do ride it WOT most of the time and at 43000 miles on a single cylinder engine I am asking a lot. Plus it does need an oil top up every week 😩

About time you got a descent engine for the Indy so just use the bike engine
Graham