'75 KZ400 factory carb issues

Hello group, 
This my first post here and I suspect I've got some fairly common carb issues to sort out.  I have a '75 KZ400 with factory Keihin carbs on it.  They are just running too rich and I can't seem to be able to tune it out.  Things I've done: 
Adjusted cam tensioner
Valve adjustment 
checked and adjusted static timing and adjusted points
Rebuilt carbs (checked and re-used factory jets as I wasn't confident in 'new' jets in kit

While the bike idles OK, the mixture screws are running 1/8" from full stop.  (all the way in).  Mixture is clearly still too rich across the board.  The bike will run decent, though a bit boggy until around 4-5k rpm, where she cuts out.  I'm effectively short shifting the bike.  While I can certainly enjoy tooling around town in this condition the bike should really be pulling much harder and revving higher.  I'm at a loss as to what to do with these carbs.  I called our local speed shop here in Madison and a carb tuning and and adjustment was $300 starting point. (!)  While I don't mind spending the money if warranted, I'm just not sure that these carbs are worth investing in.  I'm all for stock IF I can tune them out well enough, but for the cost of having them tuned I can purchase a set of Mikuni's and go from there.  I've read a few promising threads on this conversion (duals, not single) and wouldn't mind the install.   
So, I'd love some feedback from the group.  Any troubleshooting tips with these Keihins?  Are people having success with these or are they all running rich?  Is it worth all the troubleshooting and time, or would you move on to new Mikunis? 

Thank you. 

What do the plugs look like? Have you checked fuel levels in the bowl with the clear line method? 
I have been running these carbs and have not had a problem with running rich. 

Thank you Jim, 
Plugs are definitely close to fowling.  I just looked up the clear tube method and will pull the carbs and check levels.  

Best, 
Ben
 

There are a couple of common causes I've run into with the Keihin piston-slide carbs on kz400's
First, your carbs may have a rubber plug sealing off one of the jet openings. If that plug is missing, it will run very rich.

Second, I find the pistons bind easily now that they are 50 years old. Loosening the piston covers and very carefully tightening them while lifting and releasing the pistons with your finger through the carb throat will help. They should get a drop of motor oil on the sliding surfaces. The pistons should drop with a singular clunk. If you hear two clunks, o e is dragging.

Thanks for the responses everyone.  I did run the clear line test and float bowl levels are in spec.  I did make the attempt to tweak them in to the lower end of the range while I had them on the bench.  I also reseated the piston covers as there was a little clunking.  We're now in sync there.  I pulled out the mixture jets and checked the orings as well as the jets accessible from the float bowl side.  Everything checked out best I can tell.  Reassembled the setup, cleaned the plugs and got about the same results as before.  Rich.  It almost doesn't matter where the mixture screws sit as long as I have the idle turned up enough to prevent stalling.  I get a rich idle about 1500rpm and solid, if not sluggish performance to about 5k.  Mixture screws in or out don't do much.  
A couple concerns I have noticed:  Rebuild kits don't contain the pilot passage plug.  The originals still seat, but aren't tight by any means..  Also missing in the rebuild kits are the main jet o-ring  (I've purchased 3 different kits now).  Or at least an oring that seams to fit appropriately.  I'm assuming if either of these aren't snug I'm going to have rich running problems.  If I'm to fix this correctly I'm looking at quite a bit of money to buy 'new' plugs and another bit of headache sourcing some orings to fit the main jet tightly.  
Thoughts on next steps? 

 

Here is a fairly inexpensive possibility.


www.harborfreight.com/180-piece-viton-o-ring-kit-67525.html

I'll look for the dimensions of the main jet orings.  I probably have a post here somewhere.
I think I may have gotten the orings here, but by dimension, not by make and model.
They will sell single orings, which must be a headache for them.

newmotorcycleparts.net/fuel_system_parts...v_gl_carb_parts.html

Maybe check this post:
kzrider.com/forum/3-carburetor/605638-19...ters?start=24#823138

Wow, thanks everyone for pointing me in the right direction here.  I ordered a number of CVB36 carb orings in various sizes.   Figured they'd all come in handy at some point and they're rediculously cheap.  Totally hilarious they're sold individually, I'd hate to be the person putting my order together.  Loudhvx, thanks for the post link on main jet size.  I also ordered some Suzuki? pilot passage plugs from Dime City cycles which had a similar profile to what the Keihin is using.  We'll see if they seat with a little love/mojo..   I'll probably post up some install pictures when I get around to the job.  I'm actually optimistic on getting these carbs going again.  

Best, 
Ben

Since you didn't mention these things, I'll suggest that you check them out -

-Spark plug condition
-Spark plug gap
-Voltage at coils

It sounds possible that you could have some weak spark problems. 

On my old Metro, I couldn't go more than 45mph without it cutting out - after much hair-pulling, I pulled the plugs and discovered that one plug had essentially no electrode.

wrote:

Since you didn't mention these things, I'll suggest that you check them out -

-Spark plug condition
-Spark plug gap
-Voltage at coils

It sounds possible that you could have some weak spark problems. 

On my old Metro, I couldn't go more than 45mph without it cutting out - after much hair-pulling, I pulled the plugs and discovered that one plug had essentially no electrode.

Yes, a weak spark can manifest as a rich condition. Checking the health of the ignition system is a good idea.

Its been a little while since posting here.   I'm looking for an OEM rear cargo rack for my '75.  If anyone has one they'd like to sell please send me a message.  
Thanks,
Ben