Overly Rich Mixture - idle to 1/4 throttle

11.4 volts at the coils is pretty low, it should be more than 12. Perhaps there are some dirty or corroded connectors in the coil circuit. Some pipe cleaners, small brass bushes an a can of Deoxit D5 should clear up any problems there.

They look just like the brass in both sets of my 26mm carbs.
I'm running stock needle clip groove, a #20 pilot and 115 mains ...with idle mixture screws at about 1 3/4 turned out.
My wide open throttle chop, plug inspection at the side of the road says my main jets are at least two sizes small and my slow speed, off idle to 1/4 throttle will really darken the plugs ...so too rich.
I'll be reinstalling the 17.5 pilot and probably trying my 120 main jets.
I really love the highway speed gas mileage of 45mpg. But off white plug tips are a bit hairy for me.

Could re-do the clear tube test.

And also assure the floats aren't installed upside down (if that's a possibility on these carbs).

Good Fortune!

Was chatting with a mate about this problem to try and solve this problem.
He reckons that the only way the engine can get so much fuel (without actually flooding) is for the fuel enrichment (choke) system to not be disengaging.
This makes good sense and could be the problem, as the choke lever mechanically lifts the plungers and allows the additional fuel to be drawn into the engine, but it does NOT actually push them closed - this is the function of the return springs on the plunger shafts.

BING! - LIGHTBULB moment!!! - I suddenly remembered that a couple of days ago I noticed that the mounting plate which carries not only the carbs but also supports the choke shaft had a crack around the boss which is closest to the choke lever. This was probably due to the carb assembly having a fall or the bike being dropped at some stage.

Anyway, latest theory is that due to the damaged choke shaft boss, the choke shaft is no longer perfectly aligned with the axis of the carbs and the plungers are not quite concentric with the bore of their choke "ports" and are binding.
Further, that the plunger return springs are not strong enough to overcome this binding and as a result the plungers are not shutting off the additional fuel even when the lever is fully closed, with the end result that it's running on full/some choke all the time!
(I thought that I'd determined that the plungers were as far down as they could be with choke off - but maybe not!)

Have a couple of repair options:
1. Repair the plate - not best option - high risk of breaking the plate completely
2. Replace the damaged plate - availability?
3. Use stronger springs to overcome the binding - springs are original and may be weak anyway
4. Drill the shafts and insert a small pin so that the choke lever positively closes the plungers as well as opens them - maybe best option.
Subsequent to drafting this email I found a plate and have ordered same - should have it in about 7-10 days from the States.
Hope that this is the cure - and will advise progress.
Also now have borrowed an air-driven rattle gun so should be able to get at the starter clutch and do the repairs.
Can anyone confirm please if the nut on the LH end of crank holding alternator rotor and starter clutch is LH or RH thread?

Hope you are right mate - makes total sense !

Where are these choke, plunger return springs you mentioned? I can't seem to remember this....

Wonder if you Could you try and push the plungers down by hand to see if you feel them seat better ?

Tried to attach some pics of the relevant parts manual pages but .pdf scans are nogo - have to take a photo instead and attach as a .jpeg.
In the meantime and to hopefully explain - the return spring sits under the starter plunger cap and pushes against the lip on the plunger "piston" (for lack of a better word); this spring is compressed when the choke lever is lifted to the "on" position, when the choke lever is pushed down ie "off" the spring SHOULD return the plunger to the fully closed position and shut off the enriching fuel system (choke).

Good Fortune!

I'm not sure those springs exist in the carbs on my bike now. WTF?
I'm going to slide the shaft out of my back up carbs, same year 26mm, and see if they are in those and maybe I lost the in ones on my bike from years ago rebuilds.

I don't remember having them.
Steve

No return springs, mmmm.....? unless someone has put some sort of pin through the plunger shaft under the collar (to give the choke lever something to push against to push the plungers down) they will stay up and the choke will be "on." - N'est pas?