Upgrade carbs for KZ750

I never want to re-live the drama and trouble I went through to get mine cleaned and running correctly. For the record I never "unganged" them. I had them pro bubble\vibrato cleaned at a shop and the bike runs perfect now.

chopper1963 wrote:

I never want to re-live the drama and trouble I went through to get mine cleaned and running correctly. For the record I never "unganged" them. I had them pro bubble\vibrato cleaned at a shop and the bike runs perfect now.



 

I wrote a rebuild tutorial for Mikuni BS CV carbs some years ago.  This was skewed towards the Suzuki GS crowd, but 90% of the details also apply to KZ guys as well.

I've shared said tutorial hundreds of times, but you can only lead a horse to water...

Parallel, I started selling O-ring kits in support of rebuilds.  For all of $20, you can get a full set of O-rings to rebuild either a set of BSCV carbs, or VMs.

Since 9/22, when I started offering O-rings, I've sold 176 sets to GS dudes, and 34 sets to KZ guys.  

"I never unganged them" seems to be a KZ thing.  GS guys get on with the project at hand and don't shortcut.  Do the job once, do it right, and profit.

gsarchive.bwringer.com/mtsac/~cliff/stor...Rebuild_Tutorial.pdf

 

timberleek wrote:

@Daftrusty & rstnick,

I've obtained a set of GPZ600R carbs and started looking into parts differences to the ZR7 (ideal order of operations, i know).
The boots are obvious, i need those anyway.
But What internals did you use?

Looking at the replacement part numbers for both bikes. Almost everything seems to be different.
Slides, needles, emulsion tubes and even floats and float needle
With the time difference between the bikes, i can imagine some numbers are different due to negligible production differences.

Did you just change to the proper needles (N6NC & N4MD) and jets (35/108 stock zr7, 38/108 stock ZX600 and 45/112 seems common for the kz650 jobs)?

I went back and looked at my notes for carb jetting and I have a correction to make. I incorrectly stated that I am using the Factory Pro stage 2 jet kit. It is in fact a stage 3. Stage 1 is for carbs using the factory air box and 3 is for use with pod filters. There seems to not be a “stage 2”.
I only changed the needles, idle and main jets. I did not change anything else, beyond setting the float height to 17mm.  (When I unganged all the carbs to thoroughly clean them, I did change the plastic fuel pipes and T to metal ones from an older set of CVK carbs I had. I also replaced the o-rings on them as well.) 
Even if you are going to use the stock airbox, but are going to be using an aftermarket 4-1 exhaust, your pilot and main jets are going to be very different from the stock zr-7 jetting. The zr-7’s were plagued with flat-spots and bogging due to emission friendly jetting and the troublesome throttle position sensor that altered the timing curves.  It’s been years since I researched all this, but I distinctly remember avoiding the zr-7 jetting because of the info I found.
 



 

timberleek wrote:

@Daftrusty & rstnick,

I've obtained a set of GPZ600R carbs and started looking into parts differences to the ZR7 (ideal order of operations, i know).
The boots are obvious, i need those anyway.
But What internals did you use?

Looking at the replacement part numbers for both bikes. Almost everything seems to be different.
Slides, needles, emulsion tubes and even floats and float needle
With the time difference between the bikes, i can imagine some numbers are different due to negligible production differences.

Did you just change to the proper needles (N6NC & N4MD) and jets (35/108 stock zr7, 38/108 stock ZX600 and 45/112 seems common for the kz650 jobs)?

All rubber o-rings were replaced, and the jets suggested by Pablo is what I used;
"This is just for reference (already in one of the previous pages):
ZR7S stock jetting: 35/108
My setting for stated AFR: 45/112".

Odd that the jetting for a 650 was larger than the 750, but it seems to work well.

Did not change needles or Needle jets, just left them as is.
I believe the 750 CVKs have different needles for the middle two carbs than the outter two, or something else different, than the 600 CVKs which have all 4 the same size.
Just changed the Main and Pilot jets to 112 & 45 respectively.

Small update

I got the carbs, and all additional parts (boots, jets, etc).

The size (and weight) difference is significant:
 
   
So no issues at all with the petcock (which was always close to the carb) or anything.

The combination of intake boots, carbs and airbox boots are a bit shorter than before.
The old CV's measure approximately 15.5cm between the head and the airbox.
The CVKs roughly a cm shorter.
This isn't a problem, the airbox can be shifted forward by loosening the 2 screws at the sides (behind the electrics). In my case it has to go to the end of the slider, but it works.


What is a problem, the 650 airbox is different than the 750.
The hole size is smaller and the locations are different.
The conversion guide on the proboards forum shows the existing holes need to be enlarged and the middle ones slightly moved outward to get this:
 
The (unmodified) 750 airbox is like this:
 

The 750 originally has larger boots than the CVK's. The holes in my airbox are 55mm while the CVK (ZR7) boots measure 50mm.
The spacing of the inner holes is correct in my case (with the inner boots turned outward), but the outer holes are too far out.

One solution would be to move to pods, but the general consensus seems to advice against them in combination with CV carbs.

It looks fixable, so i'm contemplating those options for now. 
One idea was to make rings to glue into the existing inner holes to narrow them to 50mm. For the outer holes it would be a moon shape to close the part i don;t need while i dremel the holes out to the middle.
But i'm not sure if that will be strong enough when wrestling the rubbers in.

Plan B was to cut out 1 large hole across the 4 existing holes and glue a new cover plate over the whole front of the airbox. The i'd be free to drill new hole size and locations.
By adding a full cover plate i hope to sand the edges back to make the whole ordeal look stock again.
 

On my build I had to lower the holes 15mm to lift the airbox into line with the modified side panels.  I cut the front bulkhead out, made a new one from 3mm ABS sheet then glues and "hot riveted" it into place. Turned out OK





 

Some have made a new sheet to fit across the air box, and new holes made.
Here's one example I was able to find: