Bike won't fire

[Art]

 

If I was a gambling man I'd wager either this 'mototuning guy' has misdiagnosed the problem or you've misunderstood what he's told you. Carbon build up is mostly a thing of the past and is unlikely to occur in a modern engine, run on modern fuels, with regular engine oil and filter changes whether that engine be a CBF, a CBR or a Ford Fiesta it matters not, carbon build up is mostly a thing of the past. That's not to say it can't occur, it's just so very unlikely and can't be diagnosed by a simple compression test alone. Also I'd have expected a competent mechanic to have inspected the combustion chambers using an endoscope before jumping in with a recommendation for an engine rebuild.

For my two penneth and the benefit of our readers there are three prime suspects to cause low compression, these are valve clearances out of specification, worn or broken piston rings or a failed cylinder head gasket. Of course there are other causes but these three are the prime suspects. It's simple enough to eliminate or prove the head gasket by examination of the engine oil, coolant and in situ inspection of the head gasket seal. Piston rings and valves can be eliminated or proven by following up a dry compression test with a wet compression test, this is where 10-15 ml of engine oil is added to each cylinder before the compression test and should be carried out before any stripping down of the engine. If the compression doesn't improve by adding oil suspect the valves and a top end strip down will be needed to determine the exact fault. If compression does improve with the added oil suspect the piston rings or cylinder bores and a full engine rebuild may be on the cards.

[Stvlas]

Thanks Art,
You are also a very knowledgable guy too...... I have not got the expertise or facilities to investigate or verify either of your diagnosis.  Either way,  it strongly looked like an engine strip down of the top end.  Fixable yes.... but not by me,  and expert time, labour and tools cost dearly.  Was sad to see the CBF-F go,  but I'm also delighted with the NC750X.  Serviced correctly and regularly,  I've seen evidence of NC's doing North of 250k km. 
You may like to check out mototuning.ie.  If they don't know what they are at,  then I don't know who does?
Value your thoughts as always Art.  The Internet would be a barren place without helpful people such as yourself 👍👍😊
Stay Safe man.....
Niall...

[Stvlas]

By the way Art,
The CBF-F had accumulated 96k km.......  and always got serviced on time. Valves were done by myself 15k km ago 👍😊