Jet needle hardware question

Trying to sort a small problem with the set of VM26 carbs on my 78 KZ1000A2. The bike has a bog when you first roll on the throttle at idle. I have confirmed by use of a wideband O2 sensor that the mixture goes rich (10:1) when this happens. Unfortunately, this corresponds to the same throttle position for steady state cruise at 45mph in top gear where the bike stumbles noticably. I have the rest of the jetting right where I want it, and the bike runs really well otherwise.

So I was reviewing the parts diagram at kawasaki.com and discovered somethings that I seem to be missing. Looking at the attached diagram, I don't have parts #42, 43, or 45. I just want to verify their correct installation as I have no experience with these particular carbs other than the set that I have. If I'm reading the diagram correctly, the jet needle #17 is inserted through the washer #45 and the spring #43 and then the throttle valve #18 so that the circlip #16 rests on top of the washer. Then the ring #42 is on top of of the circlip. If this is correct, it would seem to explain why I have to use #125 main jets and needles on the 5th clip to run right. I also am running #17.5 pilots, and I suspect that if the needles were correctly positioned, then I could step down a pilot size and remove the rich condition just off idle.

Also, I have 5DL31 needles and the correct needles according to Kawasaki are 5CN7. According to my research, the 5DL31 needles are leaner at higher throttle settings than the 5CN7. Possibly supporting the need for very large main jets in a basically stock motor. OBTW I'm running the dreaded pods and 4 into 1 exhaust.

Edited to add picture.

I have a set of 76 26mm and also have the same needle in them, no washer just whats in the pics. Sorry multiple posts.

I have owned the bike for 28 years so I suspect they are original, granted its a 76 Hope this helped

Thanks Moneypit. I didn't really see how there was any room in there for a spring and two washers, but wasn't sure. Actually, the parts that are boxed in on microfiche picture have notes that say for use with 16001-1023. Kawasaki.com shows this as a carb rack assembly, but I can't find what model it fits. My bike was something of a Frankenstein when I bought it, and I can't be sure that these were the stock carbs. Oh well, one theory down the drain. If I could just get rid of that one little trouble spot, the bike would carburate perfectly.

worn needle "jet" perhaps? Not sure how you would check it though. Can you measure if your at quarter,half throttle EXACTLY? I usually put a marker pen mark at closed,quarter,half & three quarter throttle openings on the twist grip so i can have a quick look to see exactly where its occurring.

Cheers,
Kt.

Ktm181 wrote:

worn needle "jet" perhaps? Not sure how you would check it though. Can you measure if your at quarter,half throttle EXACTLY? I usually put a marker pen mark at closed,quarter,half & three quarter throttle openings on the twist grip so i can have a quick look to see exactly where its occurring.

Cheers,
Kt.

Yes, I'm actually using a Innovate LM2 wideband O2 sensor and datalogger. I'm able to log air to fuel ratio, rpm, and throttle position. I have installed a throttle postion sensor directly to the throttle bellcrank on the carbs. The problem arises from say 1% to 5% throttle. Causes a bog when you are rolling away from a dead stop, and also at a steady state cruise. Top gear, 3000 rpm, about 45 mph, and the bike is stumbling. This corresponds to an AFR of 10:1, 2% throttle, and a noticeable sucking sound from the carbs. Sounds just like when you try to crack the throttle on a cold motor still running on the choke.

I just know that I'm missing something here. The main jets are two sizes over what anyone recommends for a 4 into 1 and pods, and I have the needle on the fifth clip to keep the AFR under 14:1 when accelerating. Granted, I'm at sea level, but it just doesn't add up in my mind. It runs good, but I don't see what could cause the need for such large jetting.

I'd wouldnt worry about what the others are running,using what you have is better than what we "plug chop" at. For rich at just off idle i would be double checking pilot,needle diameter AND needle jet itself, ULP and/or Ethanol causes wear in needles and the needle jets, for wide open throttle i would just go with the LM2 setting, 2 sizes bigger main might just be the better flowing pipe and/or no baffle choking it, or might be a ported head flowing more air etc. In any case if AFR is correct up top i would just focus on the bottom, can you borrow needle jets? Can you borrow needles?

One other thing i just thought off, how much oil does it burn? And another, nearly ALL these old girls foul plugs to some extent around the throttle range you are finding problems with,you might be about to confirm the cause of a lot of wasted coil mods!

Ktm181, let me first say thanks for taking my questions seriously. As for everything above 25% throttle, I agree, it seems too big but it works. This bike pulls as well as can be expected. My head, bore, pistons, cams, valves, and carbs are stock. I do have a welded KZ900 crank, pods, 4-1 pipe, and Dyna 2000 ignition. No coil mod necessary here. I can verify full battery voltage at the coils and timing has been verified with a timing light.

We here in the Houston, TX metro area are saddled with 10% ethanol blended gasoline. The needles do not have any appreciable wear, and I only removed one of the needle jets which seemed good. I am a machinist, and as such feel that I can discern mechanical wear. I don't know of a source of needles or jets that would allow me to borrow.

As for oil consumption, I must say that I have noticed that the bike uses about 1/2 quart per tank of gas. I had no prior knowledge of this particular engine. I disassembled the engine and everything measured to spec. I did a light hone to the cylinders and re-installed the stock pistons with new rings. I was hoping that this level of oil consumption was evidence of rings that were seating in. I will say that I notice zero evidence of oil smoke at idle either cold or hot. Occasionally, there is some small, occasional crankcase vapor smoke once the bike is fully hot through the breather. The only evidence of oil smoke when running is after a strong throttle pull. When the throttle is completely closed, there is a blue/white tailpipe smoke under engine braking.

Another curious item of note is one of the cam end plugs seems to be working it's way into the head. Is this a sign of crankcase vacuum? What does that mean? I have just been through five tanks of gas since I got the bike running again. I feel that I need to change the oil, recheck valve clearances, have a look at the plugs, and test compression. Any thoughts?

Seems like your are working through it the same as i would, the smoke i would be looking into, not sure but oil might be playing havoc with your af ratio although you would think you would also see it on your plugs. I still think needle jet might be the cause OR too small dia needle, for that matter maybe a bigger dia might take up any wear in the jet, I have recently chased similar problem in VM26 carbs and it turned out to be oil although didnt have a wide band to check actual ratio. My engine is new 1075, has just done 500 miles, uses about 100 millilitres in 200 miles NO smoke at any time, although i would necessarily be too worried if it used double that, a litre in a 1000 miles is still reasonable BUT might upset af ratio if measured. Make sure you are running 20w/50 oil anything thinner might just be too thin in your engine. Your cam plug moveing is common, they need to be "glued" in, i use silicone and let them dry in place a little before fit of cover (say 15mins), you can check sump vacuum, it wont have any, it will be pushing a little out the breather,just a very small amount if rings/bores are sealing correctly. If not sure about ring seal the only way is a cylinder leak down test,you would need the right tools to do though, it measures % gases bypassing rings. WHAT does it do if you run the smaller slow jet (pilot)? AND another thought, if you end up at needle jet wear but cant get jets new, i would reckon you could machine some off the slides (establish if they are standard measurment first) as the slide cut away affects same as needle diameter range or there-abouts, although once done there is no going back! Again, lots of these bikes foul plugs in the range you are speaking about, you might just be onto something none of the rest of us have ever mearsured, i mean maybe all these coil mods are trying to cure worn jets.....run your thoughts by LarryC and see what he reckons, i just fitted CR29 Keihins at Larry's recommendation, LarryC head,1075 Cammotion cams, undercut gears etc, RUNS NICE NOW !

One other thing to be DOUBLY SURE about it to make sure the needle cannot jump up an down when its fitted into the bottom of the slide, if it can move around the biggest effect is just when cracking open the throttle,, you might even want to shim it a little but bare in mind the needle still needs to be able to move a little so as to centre itself in the needle jet.