Bike performs very strangely

Still fighting with this customer's '78 KZ650 with VM24 carbs.  This bike has pods and a 4 into 1.

Needles - 5th position
Main jet - 107.5
Pilot jet - 17.5

Not sure what happened but today the customer came to get it and it would barely run.  I've been fiddling with it, and apparently the vacuum petcock let loose.  Plugging that and setting it on Prime solved the super rich condition on cyl 2.

I'm still fighting weird fueling issues though.  To get it to idle right and rev properly (rev up and down rather than rev up and hang) I had to close the air screws all the way up.  I'm mostly familiar with Keihin carbs but it seems to me like it shouldn't run at all with that air screw turned all the way in.  Anyway, it runs and rides fine up until about half throttle then it just sits at about 65mph and won't go any faster (in 5th gear).  Pulling the plugs they're jet black.

Another weird thing, while it's idling (with the air screw all the way in) engaging the choke makes it run up to about 4k RPM.

Weirdest combination of stuff I've ever seen... Any suggestions?

Those jets are miles to big. 
Vm24 with pods. 
15 pilot jets. 
105 main jets. 
Needle clip position 4 slot from the top. 
Air corrector jets fitted. 
Bowl fuel level 3mm below mating surface. 
Plugs B7ES NOT BR7ES. 

Assuming you have quality pods and not shite ebay cheap crap with a lip on the inside that covers the pilot intake and you have decent voltage to the coils and decent compression it'll run fine on the above settings.

Hanging revs will be an air leak on the engine side. The  clamps need to be tight and ensuring no air is sucked in between carb and hose joint. Equally hose needs to be air tight to the head. Vacuum caps need to be airtight on the vac port. 

You mentioned it wouldn't hardly run due to vac pipe to the fuel tap. Are you 100% that both ends of the vac pipe from fuel tap to number two is 100% airtight. If you removed the vac pipe to number two but didn't cap the carb port it'll run like shit as it'll just be sucking in air on the carb.

Your half throttle issue is caused by the over jetting. 
VM carbs are 0-3kish revs pilot only. 
3k - 6k are pilot and  jet needles operational. 
6k plus is pilot, jet needles and needle jets operational. 

So with your current jetting it's far too rich and won't rev above 6k.
 

Also, if the diaphragm in the petcock is torn or holed. the vacuum line will suck a bunch of fuel from the petcock into that carb, making it wildly rich.

Did you mean a 15 pilot jet instead of 25?

The pods look like cheap eBay junk to me.  They do have a lip on the inside.

You absolutely nailed it on it not revving past 6k.  It had 112.5 jets in it when the guy brought it in O_o

EDIT: I did cap off the vacuum line to the petcock.  I did see it sucking fuel in there which is what keyed me into it being borked.  I doofed it on the first post and said lean instead of rich, I'll fix that.  We'll just play this game of editing these posts over and over

Yes, podgy fingers syndrome. I've edited it! 😜 15 pilots. 

Cut the lip out. Or fit some proper k&n's that actually work. 

Hunted around in my parts bin (I always pull pods off and put the OEM airbox back on my personal bikes) and found some K&N pods.  I'll just give him those, I'm not gonna use em anyway.

Ordered the 15 pilots and 105 mains.  I'll pull the carbs off again here in a few to go ahead and set the needle position.

Great stuff. Forgot to mention airscrews 1 1/2 out.
Fuel screws (if you have them) 3/4 - 1 out. 
Should be good to go 👍

Alright, replaced the cheap pods with some that aren't blocking the air passages.
Needles on position 4
Main jet 105
Pilot jet 15

Bike starts just fine, idles fine (though still rich with the air screws at 1.5 turns out).  Trying 1.75 it barely will idle, 2.0 turns out it just won't start at all.  As soon as you give it any throttle it just dies.  If you super slowly ease into it it'll get up to 3k RPM or so but it has no power at all (acting like it's lean) however doing a plug chop at 3k the plugs are wet and soot black.

This is the most frustrating bike I've ever worked on.

Did you install the air correction jets?  Check fuel level using the clear tube method?  Replace the choke plunger rubber donut seals?  

 

I did set the fuel level with the clear tube and replaced the choke o-rings.

I honestly don't know what an air correction jet is.  Have never heard of such a thing.  The main and pilot jets are both genuine Mikuni.

Because you are using k&n's there is a bogging at around 3k rpm.
Air corrector jets resolve that bogging. 
They need to be fitted in the intake port on the opposite side to the airscrews. One in each carb. 
Circled in red here. 


The only other thing that could cause the issues you are experiencing is if the ignition auto advance is not operating correctly. Can you see the ignition advance using a strobe.?
 

Ah yeah those are definitely not installed.  Where does one buy those?  I haven't had any luck searching.

The timing advance works properly.

EDIT: Emailed zed1015 to see if he's still selling them.