1982 Kawasaki KZ750 LTD Hesitation When Engine Gets Warm

I recently just got my 82' KZ750 LTD running after I bought it in December. I had the carbs out cleaned and blew out the passages just to make sure they are clear. It idles great and revs up great. I got it around the neighborhood and was excited how well it was running until it started to get towards operating temperature. It started to bog down between 2000 to around 4000 rpms. It would hesitate a lot and then eventually catchup and speed up again. Keep in mind it will only bog underload, if I try to rev it up out of gear there is no hesitation.
In all honesty I haven't actually tested anything yet, I just wanted to get some ideas of what to check in general.
The only things I've done is clean the carbs like I said before and make an attempt to balance them (I need some practice with those gauges).

A couple things to point out that may give some clues:
The pilot screws had the springs and o-rings missing. I added the springs washers and o-rings I got from a carb rebuild kit, I dont know how far I'm supposed to be able to tighten down the pilot screws, but the spring bottoms out before the needle seats in the bore.

Another other thing I noticed is that it will not run at all if I install the plugs that are supposed be below the pilot jet in the bowl like I've seen.

The current battery I have is very weak

The last thing I'll point out, but its probably unrelated, is that there seems to be an oil leak from around the head gasket. 
 

Cover up half of your airbox intake with duct tape. Does the problem still exist?
Take the tape off and open up your airbox slightly to admit more air. 
Is your problem better or worse? 

The details behind the method. 

www.motorcycleproject.com/text/the_60-40_rule.html

wrote:

A couple things to point out that may give some clues:
The pilot screws had the springs and o-rings missing. I added the springs washers and o-rings I got from a carb rebuild kit, I dont know how far I'm supposed to be able to tighten down the pilot screws, but the spring bottoms out before the needle seats in the bore.

Another other thing I noticed is that it will not run at all if I install the plugs that are supposed be below the pilot jet in the bowl like I've seen.




 

There is something wrong with the carbs.  The pilot screw should bottom out before the spring coil binds, and the pilot plugs are needed otherwise the pilot circuit won't pull fuel.  

Alright thanks for the suggestions so far, I have some time tomorrow so I'll try duct taping the air filter. 

I think the springs I got in the kit are too long, but I don't think thats my whole problem.

Now when I purchased the bike, I got another set of carburetors. The guy said its from the same bike, but this other set appears to be the newer style that does not requrie the plugs. 

This other set is in much better shape, the ones I have on the bike right now appear to be the original, but it has some brazing repairs on it, a random hole fixed with epoxy, and I just dont know how much I can trust these.
I just can't tell what these are off of, they appear to be almost exactly the same as the original, just without the passage between the pilot jet bore and the main jet bore. Two other differences to note would be the fact that these have bowl vent tees in between the carbs and do not have threads for where the main jet would be. Ref#92063A in this diagram:  Here

If anyone could help me identify what my extra set of carbs are from or how to find proper jet sizes for them that would be appreciated. The number on the side is 1739 UI 10

To possibly clarify what I am asking in the last post, is if anyone might be able to help me determine what jet sizes are appropriate for the extra set of carbs I have, because they are in much better condition.
I'll post a couple pictures of them in a few minutes.

Here are the pictures, I gotta link them separate since they show up so large in the forum. Hopefully you can see what I'm talking about with the threads not there for the main jet and the passage for the pilot not being there.
  Gallery1
  Gallery2

There are three variants of those CV34 Keihin's: the 1st that came on the 750E & H bikes which have two main jets and a plug over the pilot jet, the 2nd came on the 750N Spectre bikes and are similarly configured but have vent Tee's between the outside carbs and different needles and jetting, and the last version was on a 750 F bike that only has one main jet and no pilot plug.  You might want to search through the different model bikes and years on Partzilla so you can hone in more.  From what you say that spare set of carbs sounds like from the F bike.

www.partzilla.com/catalog/kawasaki/motor...3/ltd-shaft-kz750-f1

www.partzilla.com/catalog/kawasaki/motor...-f1/carburetor-parts

Thanks Nessism, I went through all the parts diagrams I could find on Kawasaki's website but they didn't have that one, I forgot about partzilla. They do match the diagram for the F bike so I think thats what they're off of. I think what I'll do is just see if I can order all the jets for it and just use these ones. I will still try that duct tape, I'm genuinely curious to see how that works.

Well I tried the duct tape around the air filter and it was hard to say if it made an improvement or not. It still hesitated but maybe a little less, I just can't really say for sure.

It looks like I'll only have to order new main jets(#100) for the carbs off of the F bike, which is nice. So I suppose I won't sweat over this issue until I can get these unmolested carburetors on the motorcycle.

I don't like doing this sort of thing out in the public here but I've rebuilt about a dozen sets of those Keihin's and know them pretty well.  I can go through them for you for a reasonable price if you don't like to take chances.  Mind you I'm talking about the original set, not the F set.  I've got various spare parts on hand too, like the pilot screw springs.  Send me a PM if you want to discuss some sort of arrangement and sorry to the mods here if it seems I'm hawking my wares.  Honestly, I loose money on rebuilds when it comes to the time I spend on them most of the time so please consider that...

The duct tape test result would have shifted the cause to something other than the carbs.
Was the result the same when you took off the tape and opened up the airbox to introduce an air leak?

I actually forgot to try it the other way around, I'll try introducing an air leak tomorrow when I get the chance to.

As for the carb rebuild offer, I'm really hesitant to try and use the original set vs. the set off the F bike. The original set has a hole drilled from the bowl straight into the throat of the carb in the number 1 carburetor. I think number two had a crack or something repaired with aluminum weld. Then on the "plugs" that are supposed to be there, three out four are missing so someone tapped the bottom for set screws and used that for plugs. Now I think that the set screw idea probably would work fine if there wasn't some other unknown issue with them.

I guess I want to ask if there's any advantage to rebuilding the messed up original set vs the clean set from the F bike?