2013 CB100R White
dude, you got me thinking: what actually causes blueing. I'm a chemist, but honestly, I ( still) don't know! something to do with the chrome plating and temperature. but i'm pretty sure you're right about running lean (therefore, too hot), and that can't be good for your exhaust valves... but - pardon the thread jack - the internet 'research' (about the hardening properties of chrome platings) led me to a Reddit site featuring a lot of machine guns. not my thing, at all - I'm not American! but there was a delightful little piece of humour kinda randomly interjected:So, I thought the bluing was normal. But bit of researching suggests It can be a sign of it running lean, which would make sense with full exhaust and no tune ? Or is it simply a by-product of a full exhaust system either way.
Enjoy the New Year. Damn, I can't wait for riding season to return.... maybe two months?