KZ650 VM22 carb sync question. Do you use the air mix or the adjusters?

Hi, 1978 KZ650 B2A, pretty sure it is a VM22 carb. Not that common. The adjustment screws are factory original with paint/glue markings. I hate to disturb them after all these years, but how to sync the carbs without changing them? Do people just adjust using the air mix screws to get the vacuum matching and leave the adjustments screws alone? Thanks for the advise.

If I can add to this, the VM22 is a less common carb. So here is a picture. With the office at 10 o'clock, and the 3 ribs no the side, indicates a VM22 carb. So on the bottom, I have a main jet in the middle and then slow jet to the right. Actually there are 2 slow jets stacked on top of each other. Kind of weird, but that matches the chart. Took a while to figure that out.

The air mix screw that is serviceable outside the bowl is actually a fuel adjustment. It has a pointy needle screw and positioned on the side of the header. Changing it changes the fuel. The adjustment screws above the slides are factory set. The sliders are all nice and even already. Just about a wire thickness. So even manually adjusting these, the sliders are in sync to my thinking.

I have a car sync tool with 3 pressure gauges. Normally I hook up the vacuum tubes and see if the vacuums are the same. To change any carb, I adjust the carb slider. BUT nobody since 1978 at the factory as adjusted these? ! ? Yes possible. Some videos I 've seen really don't address a VM22 and when they do, they don't mess with the adjustment screws.

So is there another way to adjust the vacuum? Is it the air mix screws outside of the bowl? Thanks for the help. I hate to mess this up by changing the factory setting.

The adjustment screws under the top cap of the carbs are to raise/lower the slides which is how you adjust the vacuum to synchronize the carbs. I would think it's possible they haven't been adjusted since the carbs were built. If the screw you are referring to is between the slide and the airbox it is an air screw, out more air-leaner, in less air-richer. If the screw is between the slide and the cylinder head on the bottom, it is a fuel mixture screw, out richer, in leaner. Changing the idle mixture does not effect vacuum or synchronization, but will effect the smoothness of idle if you have cylinders that aren't happy.

Mike

I have completed the applying of the carb kit. Would you let me know if you think I over did it.

Bike has Pods from a local guy 2 years ago but was using standard jets #90 main, #50 slow. Lower slow was a #10. The needle pin was set to the middle #3 spot. Fuel mix screw was all over the place with the 4 cyl. cyl1-1 7/8, clyl2-1 5/8, cyl3-1 1/4, cyl4-1 1/2.

Still has pods, changed the main to #97.5. My kit didn't have slow jets that worked, so still #50 and #10 lower. The needle was raised by placing the clip down 1 spot #4. I also change the spark plugs to NKG B7ES. My kit did have a fuel mix and I set all 4 cyl to 1 1/4.

The complaint was it bogged down in the middle range. The change to the needle up one spot was to improve the off throttle. The lean condition, I thought it had is the reason I used #97.5. Idle was fine before I messed with this carb. Kit didn't have a fuel bowl needles, so that was reused.

Question I have......too many changes.....just right....? Thanks for the comments.

I don't think you made too many changes. Now it's trial and error time to see how it runs and adjusting the jetting from there.

I'd perform a vacuum sync job and don't worry about the original adjustment since that was done 40+ years ago. Needless to say you need to make sure all the bikes other maintenance tasks are up to date like valve adjustment because one issue may confuse the other. I've read lots of bad things about cheap generic pods like emgo's so that's a caution in case your bike has them. Real deal K&N's are pricey but worth it from what I've read.

Thank you for the comment. First time changing jetting. My kit has #90, #97.5, then #100.5, and #102.5 . So I guess one-step-up is not even numbers.

Is the NGK spark plug B7ES too hot...should stick with B6ES cooler? Temp here in midwest usually moderate. Bike came to me with Chamion N4C.

I did check the valve clearances.
Valve gap tests.
Cyl 1 In .10 Out .10
Cyl2 In .06 Out .10
Cyl3 In .10 Out .13
Cyl4. In .09. Out .13

Spec says .15 for both In and out. One is tight over spec over the 7 others. My feeler gauges are not professional quality, jumps from .10 to .15 and nothing in between. My .13 estimate just meant the .10 was loose and the .15 wouldn't slide in. I also had trouble deciding how to purchase spacers. Not sure what a regular guy does. Order a bunch and find what works and then try to sell them back to other guys in need? For now, I left it as-is and see if cyl2 causes me trouble.

Suggestions welcome. Now that you mention the value issue, maybe I should got back and change them. In my defense, checking the clearance was the first task I did but I had bigger fish to fry. Electrical issues, coils, battery, carb cleaning. I have the time (winter delay) and better to get these right than tune fuel/air with a out of spec valve clearance. I just talked myself into it.

I will put back the carb I just rebuilt and see how it runs. Try to take steps forward and not backwards.

The factory manual for the 650, which frankly is the only one I'd trust, specifies .08 - .15mm valve clearance. The valves tighten with mileage so you have one that needs immediate attention and a bunch that may need changing next time you do them.

As for the jets, I'd install the largest main you have and try that. Better rich than lean. And a B6 plug is hotter than a B7. Stick to the 7, which I believe is the factory standard.

BTW, you can download the real deal factory manual for your bike here in the Articles tab of KZR. If you don't already have it I strongly advise you to do so.

Good luck

No eBay APP ID and/or Cert ID defined in Kunena configurationThank you Nessism. I didn't know there was a downloadable manual. I will give it a look.

I got a suggestion from another KZ650 owner that I should have put in "air correctors" instead of changing jets or raising the needle for these pods. The example I have on ebay is not for a VM22 carb though.

Do you think I wasted my time changing jets and should have used air correctors?

Picture is of a VM24 and mine is a VM22, but those shiny parts are something called an Air Corrector.

The air correctors are a refined solution when using pods or open carbs and negate the need to change any jet and needle settings from stock apart fitting larger mains.
It's the same solution that Mikuni applied to smooth the low end flat spot on their own Smoothbore racing carbs which are designed to run with no airbox for maximum flow.
I can provide a set made to order for the VM22 ( They aren't advertised on the listing for the VM22's as there is little demand for them ).
The pilot mixture screws on your carbs are fuel mix ( Not sync screws) so out to richen and in to lean off the pilot ( idle) mix ( Initially set them all mid range of the stated book setting as a base line)
Adjusting the slide heights is the only way to sync the cylinders.
The even height of the slides does not ensure that the cylinders are in balance except in a perfect world.
Individual conditions , compression etc, in each cylinder may require slightly different heights to produce equal amounts of work from them.
You need Vacuum gauges to accurately achieve this.

I am kind of stuck with the parts I have installed. I don't want to over-spend the changes. Main jet 97.5, slow jet #50 with a #15 underneath it. VM22 has a double slow jet, I found. I can always go back to the original carb parts, if I found out this setup is unworkable. Nice to know there is a technique call "air adjustors" that is available for a VM22. Thanks for the tip. I'm going to see this phase through.

I have my new intake boots and new pod filters. Both from ebay. The air filter pods are really nice. Much better than existing one. Moxi is the name. $25 for all 4 pods. I had to order some vacuum covers for the sync tubes on those boots. Surprised not included and the old ones are old and too loose. I got the old boots off will a lot of soaking. Didn't bugger up the screws too much. Impact screwdriver has no room to give it a hit. Anyway, out now. Ready to clean the surface and put the carb back on with these new boots and filters. Looking forward to see if any gas leaks. Had to get a new fuel hose too. Old one until a new one arrives. Thanks for the assistance folks.

You should only use good quality pods such as K&N, S&B, APE, Ramair ect
Stay clear of those cheap pods, Emgo ,Moxi, HI Level etc.
You get what you pay for and the cheap ones are usually more restrictive than the airbox causing rich running and air strangulation which leads to power loss.
Unfortunately i now see you have already bought them and the Moxi pods are well know for this so if/when you find the bike won't pull past 3/4 throttle you will know where to look first.

To add to zed1015, you aslo need to check the pods to make sure they are not covering the intake ports in the carb intake mouth. The rubber ring should be removable from the filter, place it on the carb intake and look for restriction. The cheaper pods have been reported to cover the ports.