1996 Suzuki VS1400 Running on One Cylinder/High Idle

Trying to get a friend's 1996 VS1400 running properly and am looking for some advice.

Currently it is idling very high and for the most part only running on the rear cylinder. If you blip and release the throttle, the front cylinder will kick in for a few seconds, stick at a very high idle (sounds like 3000+ rpm) and then drop out again.

The bike has stock air boxes, heathly boots, knock off fuel pump, and drag pipes. Jets are stock sizes. Choke position does not seem to impact operation. Compression at 150+psi on each cylinder.

I've pulled the carbs and ultrasonically cleaned the bodies and jets. Slides are not the smoothest I've felt but not stuck. New plugs front and rear with confirmed spark on both. I was expecting the old plugs to look lean due to the exhaust being removed but if anything they looked quite rich. I am yet to pull the new plugs.

The idle screws is set as low as it possibly can be, but even with only a single cylinder firing the idle is very high. I haven't messed with the air screw on the carburetors.

I have not yet messed with the carb sync. I reinstalled the sync cable with the same number of threads exposed but that certainly could have already been well out of whack. I haven't been able to find a documented bench sync procedure which would probably be a good starting point.

Thanks!