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KZ650 VM22 carb sync question. Do you use the air mix or the adjusters? 23 Feb 2021 05:49 #843911

  • Mc Tavish
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Hi johnmull, I'm gonna stick my neck out here and probably get grief from some, but you have to get over the silly thought that all the mix screws have to be 1 1/8, 1/14, 1/16 etc..
Nobody rides on the idle circuit, the mix screws are there for you to achieve a nice steady/even idle, nothing else.
Each cylinder will require a different mix so just use your ears, you will hear the rpm increase or decrease and leave it where it likes it best.
I think you are close so open them mix screws up so it idles without choke and adjust from there.
In all my years I have never seen any dual or multiple choke setups that have rigid 1/18 1/12 etc screw settings.
1978 z650C

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KZ650 VM22 carb sync question. Do you use the air mix or the adjusters? 23 Feb 2021 10:52 #843930

  • gd4now
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Sorry for coming into this thread somewhat late and for being so wordy. I have found the vm22ss carbs harder to jet for intake changes than the vm24ss tend to be. Before I address it, let me try and clear something up first. I noticed that in your early posts you indicate there is a #10 pilot jet with a #50 jet on top or below the pilot jet depending upon how you are looking at it. Later in you posts you indicate the pilot jet is a #15 so wanted to know which it is, a 10 or a 15? As the 10 IMO would be too small. (as far as I know stock was 15)

Regarding the #50 jet, to the best of my knowledge, that jet was stock only on the vm22ss and the vm24ss carbs that have only a pilot screw (not an air screw or those that had both). I have removed these 50 jets from several different sets of carbs, both 22s and 24s, without any running issues. Not sure just why they were used stock. Can see how it would sort of act as a pre-limiter of the volume of fuel pulled up by the pilot jet and would also increase the velocity of the fuel as it is pulled up. But as I said I have removed them with out any running issues noted on both stock air box and pod setups.

I think the issue with the 22s is they have the largest slide cutaway of any of the VM carbs that came stock on the 650s. Further, though not the leanest combo of needle jet/jet needle that came stock on the 650s (those would be the carbs with an accelerator pump) but one of the leaner combos and the smallest main jet of any of the stock carbs. I think all of this was done in attempt to meet the emission standards in the US. This made for a rather lean air to fuel ratio especially at idle and just off idle. Then When air box/filter is replaced with pods it just increases this overall lean mix but again especially at idle and just off idle.

Have to say even stock air box setup with the 22s has this same lean spot, which in my opinion is true to some extent of all the iukuni round slide carbs with or without stock airbox. There is a lean spot off idle, due to increase in air flow through the carb, it is just sort of the nature of this style of carb. But this lean spot is much less noticeable in stock air box setting than with pods.

The old school way to attempt to overcame this lean issue with pods, would be to increase main jet 1 or more sizes, increase the pilot jet one size, and maybe depending upon the jet needle taper(s) and height alter it up or down. Lots of plug chops, and listening to rpm changes as you turn screws. These changes would hep sort of overcome this lean condition, but not solve it fully, it is still there to some extent just like it is with a stock air box.

I have read posts here and on other sites, by and related to the air corrector jets that zed1015 is selling. I have not tried them as of yet, so have no practical experience with them, but they make sense to me. Others have indicated they solved issues for them. I can see how they help solve the just off idle flat spot than tends to be larger with pods. Many larger carbs vm29, vm33 as well and many others have removable air jets and larger or smaller sizes to try. This is not the case with vm22 or vm24 carbs. Their air jets are a pressed fitting , so not easy to exchange. I am currently not sure just what size of air jets (pilot air jet, main/bleend/needle jet/jet needle air jet, enricher/choke air jet) are used in the 22s and 24s. There may well be differences depending on the carb set, between them but I have not pulled one out or found info on their sizes as of yet. But they all play a part. Lots of time, energy and money were spent by the R&D teams with both Mikuni and Kawasaki staff to find the best , in
their opinion, jet (both air and fuel) sizes and settings. But it appears his air corrector jets help limit air to mix with fuel pulled up into the the main/needle jet /jet needle
location and decrease the over all air allowed into the mix. That makes sense to me and can see how it will change the overall air to fuel ratio.
1977 KZ650 B1
Pods and Denco header


This is my Z

OLD KAW OWNERS SMILE ALOT
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KZ650 VM22 carb sync question. Do you use the air mix or the adjusters? 23 Feb 2021 12:21 #843935

  • zed1015
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gd4now wrote: I have read posts here and on other sites, by and related to the air corrector jets that zed1015 is selling. I have not tried them as of yet, so have no practical experience with them, but they make sense to me. Others have indicated they solved issues for them. I can see how they help solve the just off idle flat spot than tends to be larger with pods. Many larger carbs vm29, vm33 as well and many others have removable air jets and larger or smaller sizes to try. This is not the case with vm22 or vm24 carbs. Their air jets are a pressed fitting , so not easy to exchange. .


Correct but neither do the VM26 and VM 28's which also have a fixed drilling or pressed in jet depending on model.
In all these cases there is no reason to exchange or remove the original air jets but simply fit the Air corrector ( which is always a smaller orifice ) upstream of them and they are left in situ.
This enables the the carb to be reverted to stock in the case of the airbox being refitted.

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Last edit: by zed1015.

KZ650 VM22 carb sync question. Do you use the air mix or the adjusters? 23 Feb 2021 15:03 #843946

  • johnmull
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Thank you gd4now for your insight. I recognize this VM22 is a special Jan 1978 emission carb so I accept the limitations with carb kits not providing completeness. Regarding the top (pilot jet) and bottom (secondary pilot) idle jets looking at the carb positioned upright. The secondary jet on the bottom is a is about the size of the main jet and a #50. The longer jet isa short tube with holes on the side. and end. My original has no marking but the spec says it is a #15. My new kit came with this secondary jet with a #10. I didn't use the new one, thinking one with out the other didn't give me confidence. I only changed the needle and the main jet to a #97.5 as an attempt to fix the bogging down of throttle.

On the good news, I got the idle to work without the choke on. Video attached maybe if it allows me.
Attachments:

    8idlegoodtrimxx.mov

    8idlegoodtrimxx.mov

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Last edit: by johnmull.

KZ650 VM22 carb sync question. Do you use the air mix or the adjusters? 23 Feb 2021 15:17 #843949

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Maybe the movie is too large.

My solution was to bump up the fuel screws 1/8 on all 4 carbs. I did get it to idle ok without any. The plugs after a 10 min run look better. I have no carbon, although I expected some. The ground electrode is white 3/4 across the top which I think says is good. The porcelain center is grayish on all 4. It did take a lot of messing with to trim back the choke and up the thumb screws. It idles better at 1500 than 900. 1200 is the goal but.

Throttle off idle has some bogging, but not too bad. Also a couple times when I throttled up to 5k RPM I got bogging. So something to continue working on. Not sure if I want to change the 97.5 main jet jet back to #90 or the needle back to #3 spot. Should go for a ride but we are snow bound here.

My fuel screws are cyl1- 1 1/8, Cyl2 - 1 1/8, cyl3 -1 3/8, cyl4 - 1 3/8. I probably should take the carb off and recount, but I am not a fan of turning in those pointy screws, they don't bottom out soundly.

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KZ650 VM22 carb sync question. Do you use the air mix or the adjusters? 23 Feb 2021 15:28 #843951

  • johnmull
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See if I can get a movie to stick

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