87 FZ600 is bucking/jerking randomly

Hey y'all, I've been having an issue with my 87 FZ600, and since they share engines with the XJ I figured I'd ask here for help. Maybe 2 months ago I let it sit in my garage in California because an exhaust stud popped out and I was too busy to replace it (i know, easy fix). It ran fine on the 30ish miles back home (just lower power due to the exhaust leak), I let it sit and occasionally started the engine and took it around my block(sub 5 min rides), I then replaced the stud and now the bike doesn't run right . It has gotten better as I've been taking out for longer rides for ~10/15 mins but it still randomly will buck like I just grabbed the front brakes, then it will get stuck at random RPMs, had it stuck at 6k..2k...whatever it feels really until it starts riding freely again. This is very pronounced under load such as up hills or acceleration(heavy or light). In neutral the bike will rev freely and sound completely normal. Since it sat I figured carburetors and took them apart to find faint hints of varnish that were in the bowls, pilots and main jet were fine, had them dipped anyways. I'm kinda lost now for what to do, the carbs sound in sync, had then done around 3k ago. Feels silly but could it be just bad gas? I topped it with fresh gas and it seems to run a hint better. I'm teasing the idea of fuel starvation but nothing in the fuel system changed besides just maybe some varnish? Help would be nice, i really love riding this bike

 

Sounds like there's still some varnish in there, somewhere.
Also...
If you've taken the carbs apart and you still think they're in sync, you are mistaken.
Every time you fiddle with them, do a proper sync as a final act of the fiddling.