Did you run a really thin wire down the air balance tube? If it’s not called that then I realise that’s not the most helpful lol.. there is a really tiny hole in that tube that goes through to the other side of the carb. Can you see if it’s blocked.. the carbs look in great condition

If you think that looks good, then the others are mint! Not a mark on them. I had forced carb cleaner through followed by the air compressor hard against it (I presume the tube you mean is the one next to the main jet which can't come off?). Unlikely to be anything left lodged in there but i'll pull the carbs off and try that tomorrow. Any other suggestions while they're off? Carb sync was best I could do in comparing the small hole near the butterfly's (don't have the gauge to do it properly). Cheers

Pull a single wire out of a wire brush. It’s the perfect size for the hole. It’s a balance tube I believe.. they can be blocked. However still leaning on the synch... beg borrow, hire the gauge.

You're a legend mate! That tube was indeed blocked! After much work with a wire, carb cleaner and the air compressor, I freed the hole and it's now running at idle

For some reason it has now made the stutter and 5500rpm worse - the stutter starts at 5000rpm now and lasts through to 8K. To add a second washer or remove the one that's in there...? I'm thinking remove...I'm getting tired of removing these carbs!

That discolouration mark I am sure was caused by water I would put them into a good quality sonic cleaner.

Don’t worry about the pulling of the the carbs - mine leaked 3 times before I managed to figure it - had to polish the float seats. Syncing them is next. If your cylinder isn’t warming up at the same rate as the others, then you truly need to start from the beginning. Assume nothing, check everything. What’s the colour of the plug? Oh and if that one is blocked, check the others...