Keihin carbs running lean?

I know this isn't a direct ST1100 question, but I'm working on my brother in law's '91 Nighthawk, which I believe has the similar Keihin CV carbs as the ST1100.

We've opened up the carbs twice now, cleaned the jets and they are clean. Fresh lines, squeaky clean tank, and added an inline filter, stock airbox, fresh air filter - stock exhaust is slightly opened by a PO. We fire up the bike, and it idles fine, but give it any gas and it dies. Even after warming it up, you can only rev the throttle with the choke on. I believe this is telling me we have a lean condition. All the jets are stock #35, #112.

There are pilot screws we haven't touched - could that be a culprit based on our symptoms?

I know that on the CX series of Hondas (500, 650) which use the Keihin CV carbs you pretty much need to put the carbs in an ultrasonic cleaner to get them clean. It sounds like a passage in the carbs is still blocked.

IIRC the pilot screws work for idle and just off idle mixture control so they could be the problem. I think the owners manual usually had a spec for adjustment: turn the screws all the way in (gently) then back out 1.5 turns etc. That should be easy to check.

How do the plugs look? Can you get past a small throttle opening when the choke is off: rev the engine at higher RPM then take the choke off? Maybe an air leak between the engine and the carbs? Has the bike sat for awhile with old gas? Did the carbs look fairly clean when you took them apart? A gummed up circuit?

I ran a lot of more than slightly opened up exhaust and that never affected lower throttle openings mainly just top end at WFO.

Maybe a bad diaphragm or two? I'm clearly grasping at straws here since the only carbs I ever worked on were my 750-4's pre-CV variety.

I'll check some of these suggestions later tonight - thanks. The bike was last registered in 2008 and definitely had some old gas in it. My ultrasonic cleaner is down right now, I think a transistor went on it.

I just found out about secondary passages on this carb. I'll pull the slides and everything again tonight and make sure I'm getting air flow through everything. I'm confident in the jets, but it must be one of the other passages. I'll pull the pilot screws too.