Maybe found my issue

KZ900 4th cylinder not getting hot and engine skipping at less than 1/4 throttle regardless of rpm. Slides all lifted with engine off. Started engine today to spray some water into carb thinking maybe a carbon problem and noticed 4th carb slide not rising until 1/4 throttle or so then popped up even with the others. Sprayed slide with WD40 and big improvement but not right. Experimenting with air screw turned it out 3 turns and skipped bad at low throttle, turned it in all the way then turned out 1/2 turn and ran 95% better. This is with no filters or air box and carbs have not been vacuum synched. Air leaking in from intake rubber may cause this?

Perhaps a tiny tear in the diaphragm.

Presuming you have the original VM carbs and not later CV's you have not got an air leak but a sticking slide or similar.
The lifter mech above the slide is spring loaded in the adjuster .
It allows some give but only has a small amount of travel so a sticking slide is forced to lift once this is taken up.
There is also a possibility that the lifter for that slide has the spring missing or other issue with the linkage under the cap which is allowing that slide to hang behind the others.
You need to inspect that carb to identify the issue.
If it's just the side sticking they can often be eased with a polish of the slide and it's bore with some fine metal polish.

 

Thanks Zed, carbs are actually Z1B carbs. The WD40 seemed to fixed slide hanging down for now. What’s the deal with carb working better with air screw 1/2 turn out from bottom? Same jetting in all carbs the other carbs have screws 1-1/2 turns out. 17.5 pilots and 120 mains, no filters at all for now.

Those are mechanical slide carbs.  You have a serious problem if the slides don't open all the same.  I'd bust down the carbs and figure out what's going on.

All slides on VM26/28 (Z1B/KZ9001000) carbs are connected together with the main throttle shaft and are not vaccum accutated.
Remove the carb top caps and check the shaft screws are all tight.

 

Had the same problem with a set of carbs, turned out to be a carb body had a dent not visible from the outside but had a witness mark inside, polished it out, good as new, in fact the carbs had no signs of wear so must of been removed a long time prior to my chancing upon them.

mvent wrote:

Thanks Zed, carbs are actually Z1B carbs. The WD40 seemed to fixed slide hanging down for now. What’s the deal with carb working better with air screw 1/2 turn out from bottom? Same jetting in all carbs the other carbs have screws 1-1/2 turns out. 17.5 pilots and 120 mains, no filters at all for now.

The air screw only affects the pilot circuit so having to richen that on the AIR screw may indicate you are slightly weak at the bottom end on that cylinder.
Possibly an air leak at the boot.
As for running open carbs or pods you will have better results fitting air corrector jets and turning down the jetting.
You will get crisper response, more power and more mpg than the out dated sticking plaster method of upping the pilots and lifting the needles.
 

TexasKZ wrote:

Perhaps a tiny tear in the diaphragm.

I made this suggestion based on my assumption (yes, I know) that this could not happen with mechanical slide (VM) carburetors. Seems like something would have to be seriously out of whack with the linkage for one slide to move independently of the others.
As for the mixture screw, could the tip of that screw be damaged or missing? Could the passageway have been hogged out by a too violent cleaning?

Thanks for all suggestions I will check them out further, my goal was to get it running and determine if there were any mechanical problems, seems A ok, now it can start coming apart.