Ok, so I would have had an MOT this week, save on starting up me bike it's all cough cough crappy idle and kaput, same, same, piss off mate not starting for ya.  Also the Neutral light wasn't lit.   The usual pulling things apart and poking with continuity tester, revealed the neutral switch wasn't (replaced and working fine).   Initially got to thinking the head gasket had blown, leaking coolant into the engine, as I'd noted my refilled post filter change oil was now over the max line.   Today, noted that it smelled not of sweet stuff, but petrol.  Also it's really hard to discern the max point of the dipstick because of the reduced viscosity but it's easily 2" over the max line where before it was filled to a few mm below it.  Wasn't expecting to see petrol in the sump.  Interestingly, noticed that I could see the petrol evaporating out of the removed oil caps.  Read on the net it could be an injector stuck open.  Had the injectors out when I suspected they were stuck closed, so unsure what I can do to either be sure they're stuck open or if some kind of partial not quite closed when under pressure issue?   Wandered off while writing the above, due to the realisation that my new clutch friction plates were sitting in petrol!  After dropping the oil, getting around 1L of extra 'oil' aka petrol, flushing through some clean oil show a fair amount of very fine black particles.  As I've changed the clutch plates recently, I'm hoping the gunk was residual and not the friction material from the new plates.   So, could it still be the head gasket, or something similar in that 5 spanner black box or are injectors the thing?   Also the neutral switch failing seems a bit random, not entirely sure, but it almost looks like the mechanical contact that sits in the gear divots/neutral plate is lubricated.  The switch after removal didn't have continuity, so thinking it was damaged by the petrol.