1983 KZ440 LTD Idles fine but once rev'd up above 3K it will hang at 3k.

Looking for any and all help with this old KZ...To begin, before I did some work to it the thing is basically as is from factory. No crazy mods done by me or the one previous owner. At the start of last summer I noticed it was leaking oil quite badly around a few of the engine seals so I decided to replace them. Im fairly handy, grew up working on racecars, do all my own work on my cars etc. I replaced all of the gaskets down to the top of the pistons through the head of the engine. Re timed the engine, put it all back together. At the same time because of how bad these old carbs are I put a carb kit through it, and got it running.This is where the issues start, it ran 10/10 before that. When I first fired it up It would get hung up and stick all over the rev chain. Rev it up to 7k and it would come down, stick at 6, then stick at 4500, stick at 3, etc. It was random where it stuck and it would hang there for a while. At 3k it would sometimes stick forever and Id have to shut it off. Called up a local shop and they recommended new diaphragms. Put that to it, plus made sure the rest of the carb was done right. Fired it back up, similar issue, called them back. The guy there said its getting air somehow, from where though I have no idea. He then said we could try putting a small bead of silicone around the carb boots on the engine side, and even a small bead around the glue point of the diaphragms, I also made sure the throttle cable was done up with just a touch of slack in it so its not sticking. Tried that and that leads us to today. When we did all of the original work we also added a small gravity fed fuel filter to the main fuel line, is it possible were getting air there? Now, it wont stick anywhere but right around 3k every time. I can get it to come down the revs by dropping the idle screw, putting a little load on the engine by going into first and just letting the clutch out a bit, or by shutting it off. Going to give the bike shop a call back but theyre fully booked till the end of June so he was trying to give us things to do in the mean time. I also sprayed it down with WD-40 to see if it would drop RPMs and identify where the air leak was, was recommended by someone in a different sub, that didnt drop the RPM so am I dealing with a vacuum or internal air leak?At his point ive done everything I can think of other than consulting God... Any help would be great!

See if it is one cylinder or both are causing the problem. On one cylinder, put the plug boot on a spare grounded plug and run the bike on one cylinder. Then reverse things to run on the other cylinder.

How have you synced the carbs ? what "carb kits" have you fitted ? are the carb to head rubbers the originals ?
PS: air in the fuel supply is irrelevant

Hey got called away for work so I wasnt able to reply/work on it sooner. It was a Z1 Enterprises carb kit that we put through it, but we also did new diaphragms as thats what the local shop recommended as well. The carb also has new engine to carb, and airbox to carb boots on it that were ordered off amazon. Ive done a WD-40 test where I started from the front and sprayed to the back to see if anything dropped the RPM indicating a leak but I didnt find any spots that did. This morning I also tried to plug both of the vacuum ports with new plugs and left the petcock side open and ran it on prime to see if I had a vacuum leak in the line somewhere and that didnt make a difference. 

Thats a good idea! Ill put a plug on ground and give it a shot later tonight or tomorrow when I have the time to head back out to the garage 

Forgot to add this in my last reply. The carbs have not been synced since we put a like factory carb kit in it. I thought it would be that as well but after talking to the local shop they said that can cause issues but none of the issues were facing so they eliminated that as a possibility. Are they wrong could carbs being out of sync cause it to idle fine, run fine through the RPM chain when driving but always hang up at 3k? 

kinda out there maybe, but did you check the return springs on the throttle? I'm not super familiar with the carbs you have.
or could it be the main needle hanging in the bore of the main needle jet?
is there a different outcome from a very slow rev up, compared to a quick blip?
what about the choke circuit? is it pulling air there?