Revs going haywire at low end/low speed

[MiserMiner]

The history of this bike is a big question mark. Previous owner said it needed nothing and he was riding it every day, but now it seems he was lying about everything. I had a shop do the forks and sync the carbs alongside a basic inspection/tune up.

It starts great and sounds and feels amazing at highway speeds. I didn't redline it but it felt really good in the mid-upper RPMs. But cruising around the city in some stop & go was a nightmare, something is wrong. The RPMs are all over the place. Idle is a bit rough and the tach drops every few seconds causing a shake. Throttle response is super erratic in the low range. Bike stalls occasionally when not in gear and sometimes the revs go way up when I pull the clutch in, even with zero throttle. I've had to hit the kill switch to stop the runaway revs multiple times. It also gets into chugging cycles which toss the bike back and forth.

This seems like an obvious carb issue, but I'm not sure what specifically. I upped the idle to 1100 and it helped that a bit, but the revs are still going crazy on me, the bike is not rideable. I was going to run a can of Seafoam through it but this seems like much more than dirty carbs. Reminds me more of when I had a broken carb needle on an old motor scooter.

Any ideas?

I've got a Clymer coming at the end of the month and I will rebuild them at some point, but I don't really have room on my plate right now (I don't have a garage and so will have to be quick about it). Anything I can do right now without fully getting into them?

[FJmonkey]

Just to be clear, when you say revs up, you mean the engine turning over faster. Not the RPM gage bouncing around. Sounds like a vacuum leak. Possibly the diaphragms.

[MiserMiner]

Yeah. I mean the tach is bouncing but it's the engine going crazy.

Also might be important to note that this got worse on my second ride. The runaway revs wasn't happening the first time I took it out and the engine wasn't quite as erratic. Possibly due to the idle adjustment, but also maybe whatever is wrong getting worse (leak, blockage etc.)

[gpspl]

Are all cylinders firing? Get a wet rag and touch every  header to check.
If yes check if there is a vacum leak. Spray a bit of starter fluid around intake boots if rpm changes or engine dies you have a leak

[fj1289]

A bad battery can also cause ignition issues at low revs too. 

Ignition and carb issues have a nasty way of posing as the other!

[MiserMiner]

Are all cylinders firing? Get a wet rag and touch every  header to check.
If yes check if there is a vacum leak. Spray a bit of starter fluid around intake boots if rpm changes or engine dies you have a leak

I looked up vacuum leak symptoms and this seems possible. Gotta get some fluid to try this with and I'll report back eventually.