XJ550 Runs/Idles Terribly

So I've got myself an XJ550 project I'm working on, and the bike runs super rough. Carbs are clean and I've done the valve adjustments already. Those are both all good. However, the bike has a real tough time starting (though granted its a tiny bit better after the valve adjustment), and once it is started it doesn't idle right. It wants to idle around 2k rpm; when I adjust the screw on the carbs to lower it, the engine knocks a little above 1k rpm. Also, whenever you do a quick rev and shut the throttle back off, the bike hangs at 3-4k or so for a good 5 seconds before returning to the 2k rpm idle it has now. Any suggestions as to what could be going on here? Anything would be helpful at this point. Been fighting it for a while.

 

Yes you have a vacuum leak , first check your intake boots are they weather cracked? If you can get bike running spray around boots with carb cleaner if bike revs up there is your problem. Check the caps on the boots make sure these are in good shape. Cheers

 

The hanging idle is sometimes corrected by a running sync and tweaking the mixture slightly richer.

 

when i tested for vacuum leaks with carb cleaner or starter fluid or anything like that, my engine speed actually slowed down upon finding leaks and did not speed up. just something to watch for !

 

How often is this the solution? Just checked the carb boots for cracks and put new gasket on them, so it shouldn’t be a vacuum leak as others suggested.

 

the fact that it eventually does return to 2k idle suggests it just needs some final adjustments.
running vac sync and slight opening of the mixture screws

throttle shaft seals are another place where tramp air can enter.
If you haven't tried tweaking the mixture screws and performed a running sync then I wouldn't be chasing new throttle seals yet.
Anytime valves are adjusted a running sync will be necessary.