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I got the bike out yesterday at last, carbs cleaned and balanced, all standard settings, new air filter, all O rings and gaskets replaced to carb holders and airbox etc etc, new oil and filter, new plugs blah blah, you get the picture, bike picks up nicely from 5 - 6000 and will rev very smoothly to the red line.
She picks up well enough at low revs to allow overtaking in 6th most of the time.
The only slight niggle is on slow down to idle, the odd time she wants to stall, revs drop below 1400, rich?, but the odd time the revs hang on 2000, lean?
Most of the time she idles fine, any ideas what might cause this?

Mine is also indecisive at low revs. Depends on how long she's been running and how hot it is outside. The revs like to sit at 2000 or 1200 odd depending.
I wouldn't worry about it so much so long as it's not cutting out.

Indecisive is actually a good way to describe it Mr G, but when the revs decide to drop, the bike is going to cut out, I'm blipping away 2 stroke style to keep her running, sounds great, but is rather annoying, in my oncoming oldness I'd rather she would just bloody idle as I slow down, I'd rather have full concentration on junctions etc, not my engine stalling. It just seems strange that it either under or over idles, but idles nicely 95% of the time.

My old Zxr used to do that! On the way into work it would idle at different revs at each set of traffic lights and it would want to cut out if I was high in the revs and then stopped.
Unfortunately that bike is no longer with us because of my stupidity so I never did get to the bottom of what it was

Hanging revs are a sign of the inlet rubbers leaking.

A test i did to show you all:



Some people get away with a bit of gasket sealer between the rubber and the block, otherwise they need replacing.

Cheers Rob, I've already replaced the O rings to the block, the carb holders were fine too, bike had sat for years and was covered in old petrol residue, so everything was stripped, cleaned and replaced. These were leaking before the work, bike was horrible. One possibility regarding the carb holders to the block would be when I refitted them I didn't have a torque wrench that went lower than 10N/m so I may have slightly over tightened them (8.8N/m I think they should be), I wonder if this can crush the O ring too much and cause a leak, will test them again, but as i said above the bike runs really well apart from strange idling say 5% of the time I added some Redex to the tank before my last run to give the fuel pump a rinse out, can this sometimes affect the idling as its doing its thing?

The fuel pump wont affect the idle because that just keeps the float bowls of your carbs topped up. The only way that would cause it is if wasn't filling them. It then your bike would splutter and cut out if you revved it. But some redex can't hurt anyway

Silly question but I'm guessing sitting in neutral or with the clutch in doesn't affect the revs?

When you start her up cold does it start misbehaving immediately or only once it's warm?

I take it you balnced the carbs up after all that work?

I'm kind of clutching at straws with the Redex thing Smousley, never really thought this would be a problem, as for cold starts Mr G, no problem, seems to start best of a little throttle then add half choke and she idles fine, as for sitting in neutral with the clutch in, no effect on revs, but, If I am tootling along at 60 say, and hold the clutch in she will stall, certainly the last time I tried this she cut out.
And yes Rob, carbs were balanced both times I've adjusted the carb settings, they were miles out when I got the bike, used a Morgan protune.

Ran her 40 miles today, a few slight idling issues, sorted with a blip, so that is my answer, rider input required, it is a supersport, a bloody good one at that, so stop moaning KK and enjoy it.

Seems if you thrash her (responsibly) and let her do her stuff all is well. I've been told this already btw, sorry cargo

That's the conclusion I came to with my last one that did this, I got used to knowing when it was going to cut out anyway so I knew when to hold the throttle slightly just out of interest, in the first 15 minutes of running does it idle differently every time you stop?

No, first fifteen minutes it idles fine, will try to stall on first slow down, but as you say it's just a matter of catching it, I reckon she is just a little moody, and likes to let me know when I'm not letting her do her stuff, one of my Scoobys was like this, if you didn't give it the beans regularly it would splutter and huff, once you hit the loud pedal though, happiness was restored

Aah I had such a problem with mine idling while warming up!
Haha! They do love a good thrashing every now and then (all the time )