I just went though and refurbished the carbs on my 81 GL1100I.
These carbs are more complicated than any MC carbs I've worked on. You can thread tap the end of the slow jet for 4-40 put in a screw and then pull the slow jet out by pulling on the screw.
Don't overlook the air cut off valves. I'm not certain it will cause your direct problem description. But, all four of mine had dissolved in today's ethanol gas (as well as 3 of four idle jets clogged).
These are CV carbs, so the vacuum lift may also be an issue, as the carb tops are size matched to the pistons which do the lifting. They must be replaced as mated pairs and not swapped around with other components.
I went with Randakk's complete rebuild master kit. All the rubber is replaced with Viton which will withstand ethanol gas without deterioration.
Mine ran on two (poorly) before the ohaul, IF you kept blipping the throttle to keep above 2K RPM. After ohaul it idled and ran well on all four.
On yours, you might try a carb synch before digging into the carbs. The cylinder closest to the fuel pump is # 3 and is the master carb with no carb sync adjustment. Perhaps, the last carb sync wasn't done correctly?
Cheers,
