unburnt fuel is ok? unburnt fuel = less power = less fun!

Presumably by "ok" he means it doesn't require new cylinders, pistons and rings ;)

Correct

Turns out I dont think this is unburt fuel now.

One mate thinks its a valve stem seal.

So, I may have a stem seal damaged as the bike is smoking on part throttle.

Does anyone know if the stem seals can be changed without taking the cylinder head off?

I don't have an exploded drawing showing the arrangement.

If the stem seals are pressed into the valve guides then I would think the head has to come off.

Here you go....

Thanks for the drawing.
It doesn't answer my query regarding replacing the stem seals only - ?

Alright Mr Picky!! ;)

I think he maens the rubber valve stem seals rather than seats or guides.

Yes thats it, the rubber seals.

But I wonder if I should just take the engine out & check the rings as well?

I suppose a compression test will show which cylinder but won't tell me if its valves or rings?

Need a Leak down test done
Then if the pressure drops you can listen for the air leak