1976 KZ400 CVB36 tuning

Hi all, I’ve recently acquired a 1975 KZ400D. It’s up and running now but suffering from bogging down just off throttle, maybe at 1/4 opening, it does pick up after a second or so and runs nicely. Also stationary it struggles at around 3k to 31/2k rpm, runs very lumpy, higher or lower revs it is ok. It idles fine and mixture was set with color tune.
I’m guessing it is rich at low to mid throttle ranges, slightest touch of the choke will instantly kill the engine.
I've cleaned carb thoroughly and got a rebuild kit etc but 
I’m struggling to find info on properly tuning these carbs or even what the stock jetting should be, carb has 752A stamped on it. 
Any one have experience of these, any stock jetting info or advice would be really appreciated.
 

Stock jetting is at the top of page 103.

www.kzrider.com/filebase-alias?task=down...id=1231&catid=11&m=0

A possible part of the problem could be leaking starter plungers. They have a rubber plug at the end that hardens over time, and can leak fuel even when the choke lever is in the fully off position.
Do you have the factory air filter box in place and hooked up to the carbs? 

What brand rebuild kit did you use? Some of them are absolute junk. If you installed aftermarket jets and needles, you may be better off cleaning the old ones and reinstalling them. Most of the time, all that needs replacing are the orings and gaskets.

Thanks, I missed that bit in the manual.
I came to the same conclusions on the kit quality and put the original jets back in and just used the new seals.
The airbox is standard and fitted. Float levels checked with clear tube. Checked for air leaks.

Could be choke plungers (16016-015) but they seem to be unavailable though, at least in the uk/for a sensible price. I wonder if anyone has found alternatives? they seem a fairly common design, 
I did find  www.z-power.co.uk/choke-plunger-triple-models which look very similar but no idea if they will fit.

btw when it bogs down on throttle opening it does seem to recover quite quickly and then accelerates just fine, so any other things to look at whilst I have the carbs off again appreciated.


 

Pjm47 wrote:

Thanks, I missed that bit in the manual.
I came to the same conclusions on the kit quality and put the original jets back in and just used the new seals.
The airbox is standard and fitted. Float levels checked with clear tube. Checked for air leaks.

Could be choke plungers (16016-015) but they seem to be unavailable though, at least in the uk/for a sensible price. I wonder if anyone has found alternatives? they seem a fairly common design, 
I did find  www.z-power.co.uk/choke-plunger-triple-models which look very similar but no idea if they will fit.

btw when it bogs down on throttle opening it does seem to recover quite quickly and then accelerates just fine, so any other things to look at whilst I have the carbs off again appreciated.



 

Reach out to member Zed1015 - he is UK based and refurbishes choke plungers (not sure if he does your model) for a very fair price

Try Zed1015, he has refurbished a couple of sets of choke plungers for me, excellent job and highly recommended.

The choke plungers on these carbs look much different than the common VM and BS mikuni plungers.  I don't see a rubber piece?  Is this true?  

I believe there is a rubber piece, it’s recessed a bit in the end of the plunger so very hard to see in most pictures.  But I haven’t got the carbs off at the moment so can’t check for sure yet.

I think the main problem is sorted, one of the new o'rings on the main jet wasn't sealing, the jet just fell out when I took the float bowl off so I guess the o'ring wasn't doing much. I didn't have exactly the right one to hand but made one to fit good enough for now. Fired it up and the hesitation has gone. Lesson learnt avoid the cheap rebuild kits.

I will still get the choke plungers sorted at some point as they aren't great.

Thanks for the help.