1982 GSX400F intermittent running issues - what next?

[Kayak23]

How do.

I've had this 1982 GSX400F for over a year now, and seemingly spent much of that time chasing niggly little running issues.

https://farm5.staticflickr.com/4393/37157511851_3bba63e315_k.jpgUntitled by kayak23, on Flickr

The first issue I got stuck into was chasing a hanging idle. Checked the usual suspects, spray on the intake boots etc, and sometimes it would indicate a leak, other times not.
I ended up replacing the boots about 2 months ago and to be honest, it ran ok, but still not great. The idle adjust screw seems to have a very narrow window where it's either too low and the bike dies, or too high and it soars.

I ended up doing all sorts of checks, compression and leakdown and about 4 months ago, decided to do a top end rebuild and changed the piston rings, checked my valve gaps and all of that. I also completely dismantled the carbs and ultrasonic cleaned everything, cleaned and re-oiled the air filter, changed the oil and filter, cleaned and checked the petcock etc etc...

I rebuilt it and...meh, it ran ok, but still I didn't have a reliable idle.

More recently, my indicators died, so I did a load of electrical tests and found I had a suspect stator and battery. Replaced both of those and initially I thought that all my issues had gone away!

But no...

The main problem I seem to be having is that in slow-speed running, so traffic usually, the bike bogs down something chronic......sometimes.

Sometimes it's great and I can even stop nursing the throttle at the lights and take my hands off, but often it just bogs and bogs and will die if I don't keep the revs up. As soon as the revs climb in first gear it comes back to life and I'm away again and all seems good.

It runs pretty well at higher revs, it's just these lower revs situations that it seems to bog down badly...but not always, only sometimes.

Since I changed the stator and battery (only last weekend) the idle has been waaay more reliable, but then yesterday while riding into stop/start Birmingham, it bogged down really badly and I could barely keep it going until I pulled away again it mostly behaved.

So I suppose that mostly points to a problem with the low-speed/idle circuit?
But as I say, this has all been cleaned, blown out, soaked and ultrasonically cleaned more than once.

Is there anything anyone can suggest might be the culprit I could try?

I'm beginning to think maybe I should throw it off a cliff...