'81 KZ750 CV34 Carb tuning questions.

Hey everyone o/ I hope I'm posting in the right place, I pretty new to using the forums.
So since last time I stopped in I have got around to fixing her up a bit, but due to my lack of experience I seems to have created another problem while fixing others.

-Background-
My issue is before hand the PO had knocked out the baffles in the stock exhaust and really cheap pods on it that block some of the ports on the carbs... so he didn't re-jet "because it ran fine." (Stumbled from idle to 3k basically.)

-My Endeavor-
So the bike is a 1981 KZ750H LTD/4 cyl. with new K&N pods and a Delkevic 4-1 exhaust.
New plugs and wires, gapped.
I have done the valves and rechecked the clearance after 1k miles, still all within spec.
I have synced the carbs using 2 manometers.
Cam timing/chain is correct, triple checked.
I installed new pod filters and had to change out the jets to enrich it a bit. While I was in there I set the fuel levels to spec using the clear tube method, leveled on a bench.
I set the pilot screws based off the idle drop method, and currently the bike starts, idles, and takes off from a stop better than it ever has, since I've owned it.
New jets are:
40 pilot (about 2 1/2 turns on mixture screw.)
70 Primary (?)
140 Secondary Main(?)

tl;dr
While riding, engine "sputters"(not bogs, almost feels like hitting a limiter) at 3/4 throttle in any gear with load. Mostly in 3rd and up.
Normally around 6k RPM.
If I back off the throttle it will pick up until it hits the 3/4 wall again at a higher speed.

The mechanical advance is full advancing and is in great condition/lubricated. I have another bike I can swap coils over from if need be. I'm almost certain this would be a carb problems as it wasn't an issue until I swapped jets.
My plugs are tan, but I have yet to do a plug chop.
From anyone's experience, is 140 secondary mains too large? I had seen some posts that 40/70/140 was a decent setup for pods and exhaust.
This feels a bit different from a "bog" or loss of power.

I have a couple things I would like to try, but I would love to hear anyone's opinion on it.

Other than swapping coils, I'm going to try removing the baffles from the 4-1(couple screws) to see if improves, if so I will go down a couple jet sizes on the secondary and one on the primary possibly.
Also other than needle taper, which jets control the mixture the most around 3/4 throttle?
I kinda stumped. Thanks in advance.

I got around to testing it and it seems a bit better without the baffle so I'm going to step the secondary down a couple and see what happens.
Just got a ultrasonic cleaner a few days ago so I also cleaned, and synced the carbs again. Also went ahead and replaced all the old fuel transfer and bowl orings.

I came across an older post talking about the CV34 oring sizes from Undiablo. Nessism said he'd try the 67 ID x 2mm CS(cross section) rings as well. I just want to say, the 2mm's seem to work great.
I will link that post incase anyone needs it.

CV34 o'ring sizes

From anyone's experience, is 140 secondary mains too large? I had seen some posts that 40/70/140 was a decent setup for pods and exhaust.

I've run 35/70/140 with K&N pods and a MAC 4->1 exhaust on my 1980 750E1 for several years without any problems . I now have an airbox and Delkevic and I think the Delkevic if anything may be a smidgen more free flowing than the MAC so your jetting should be fine and certainly not to large.

Download a copy of the manual here. Click the Articles tab, Service Manuals and select the GPZ750 Base manual. At approx page 150 there is and excellent description of how the carbs operate. At 3/4 throttle and up, everything is running on the main jets (needle, primary and secondary) and also dependant on proper operation of the diaphragm and air jets. You may need to inspect and clean if necessary.

You say "not bogging" so maybe electrical? low battery voltage ? low voltage at coils? poor electrical connections ?
Check voltage at the coils with ignition on and bike not running.

PS where did you purchase the #40 pilots ? Was it these ones from Jetsrus www.jetsrus.com/a_jets_by_carburetor_typ..._keihin_3M_slow.html
No problem with these. ...... except maybe the $. Just wondering if there may be another source.

My next best guess then would be, try to clean all the connections and run through the electrical. I havent had the chance to swap the coils from the other KZ.
Also, I did purchase the #40 pilot jets from Jetsrus. I feel they're a little steep but its the only place I've seen offer them.
Ignition problems always seem kinda rough to track down... I may swap a couple things to diagnose if the electrical checks out.
Also I will definitely check out the GPZ750 manual.
Thanks for the resource and I will post back with any info.

So I went out to the garage before hitting the hay tonight(I'm on my phone) and I wasn't getting any resistance over the plug side of my left coil, at all. At first I thought my multimeter had died on me but I was getting readings off of 3 other coils and not that one. So Im gonna start off tomorrow swapping coils.
At 4k rpm its at ~14v to the battery.
I had 12.3-12.5v at the battery(ignition only, headlight off), 11.5v to the front of the coils. The readings were all checking out except the no resistance on plug side.
Just odd...
I'll post back tomorrow.

Bad coil? Bad plug cap? Bad plug wire/HT lead? Bad connectio between all 3 components?

JR wrote: Bad coil? Bad plug cap? Bad plug wire/HT lead? Bad connectio between all 3 components?

Well I put it in the trickle charger last night and double checked all my coil connections. It seems it was my 2&3 ignition coils breaking up. I swapped it with the other bike's coil and I haven't had a problem on this last ride. So that may have well been it.
The plugs are new and the wires are very new as well.
I'll take it for another couple spins and tell you how it goes. No bog, but definitely was ignition related.

I'd be interested to know if your problem disappeared. I'm noticing the same thing on my bike (1980 750H, stock air box, stock jets, Delkevic megaphone exhaust). It seems to be at about 1/4-1/2 throttle but only above 5000rpm. If I open the throttle right up it will pull fine to about 5000 rpm, then the sputtering starts. If I then roll off the throttle it calms down.
I have recently swapped out the coils for new ones from dyna. The wiring was completely redone and the jets are all new. After reading the manual I'm thinking my problem is maybe a stuck slider or a torn diaphragm.
Please let us know if the new coil sorted everything out.

Hey Calum, I will try to go for another ride today and get back with you. From what I can tell, yes it fixed it.
If you find anything out about your sputter jeep me informed.
Have you pulled apart your carbs before? Just don't be me and drop a slide and bend a needle. That sucked, haha.

So I tried a few things out on the way home. It seemed to be a bit better after I was a bit heavier on the throttle for a while. I'm still losing power when it starts stuttering at about 5500rpm. It's almost like one or two of the cylinders aren't firing correctly but could also just be due to the timing being off. I'll check the advancer shortly and make sure it's rotating freely.
I think it may be a sticky slider. I'm basing this on the fact that it runs smoothly again from about 7000rpm on. I figure that the vacuum is strong enough at 7000rpm to get the slider moving. Is there any way this would show up on a vacuum gauge (e.g. lower vacuum on one carb when revving)?

@M1zore: I recently did a complete rebuild of the carbs. This is why I'm thinking it may be the sliders. I'm just not sure how to localize the carbs that are causing the problem (or the prove that it is actually a carb problem.

EDIT: Probably not the timing as the problem is throttle dependent. If I don't open the throttle up it runs fine, when the throttle is opened up it starts stuttering straight away. If it was a timing thing I would assume it would just be dependent on the rpms, not rpms and throttle. Does this seem right?

That seems right to me. That makes me wonder, are you running the Delkavic with the baffles in or did you remove some? It could be a jetting issue...
Do you have the same CV34's as me? I found out on here that there are two CV34 models. One with pilot and main jets and one with pilot mains and secondary jets.
Also on the carbs I always found the "slide drop" test to be pretty good at telling me if it was catching or operating smooth. Getting the intake booth out of the way can be a pain but I wouldn't see any harm in polishing the slide and bore maybe. I don't want to give out bad advice but I would use an extremely fine metal polish or 0000 steel wool if the were any nicks or rough spots. I'd check bent needles and this may sound weird.... but also I would check the emulsion tube to see if the top is bent. I was working on a KZ and the slide was sticking closed. Turned out someone had over tighted it and somehow bent the tube where the needle seats. (Same bike that the PO had stripped out some spark plug threads. I would assume he was a bit heavy handed.)

Also I meant to say I feel like it might show up on a vacuum gauge as a higher vacuum because the slider would be stuck down restricting air.