Rejetting CV36 Keihin carbs for a KZ400 B2 engine

Hi,

I have a stock kz440 A1 that comes with CV36 Keihin carbs but I have a KZ400 B2 engine in the frame. My airbox is stock and exhaust is a decent Sito aftermarket.
It idles fine and have a good mid-range response but I have no power when I go full throttle. A plug chop showed sooty plugs. From what I gathered, it means it's too rich.

Would a change of main jet be sufficient to solve my problem, by going down in sizes ? Do I need to tweak the secondary jet as well ? What about fuel level in the bowls, will I need to play with those as well ?

My primary main jet is #70, secondary #85 and on these carbs the needle doesn't have any clips to adjust its height.
Any help would be greatly appreciated.

The KZ400 engine runs with Keihin VB32 carbs it seems.

Thanks all

Here is a pretty straight forward way to approach carb tuning.

www.factorypro.com/tech/tech_tuning_proc...igh_rpm_engines.html

Texas Kz - a million thanks for the CV carb tuning link! Trying to revive an '83 ZX750 frankenbike I bought in a basket (should have Mikunis but has Keihins) and was looking for a step-by-step rational approach to setting up the carbs. Got it going and couldn't get it to idle - running very rich. Replaced boots to eliminate air leakage possibilities and adjusted float heights - apparently wrong as it burbled and stumbled at 2k rpm and wouldn't rev under load on the first test run. Back to the drawing board but now armed with valid info - thanks again!

Of course, carb tuning is the last thing on the tune up list. Valve clearances must be to specification, the ignition system must be in spec, the air filter must be clean and in place, and all of the carb boots (both sides of carbs) must be supple and free of surface cracks. If you try to adjust the carbs to make up for any defects in thes other areas, you will end up having to retune the carbs.

Did the Keihin carbs had the rubber plugs on the pilot jet port. If not the engine will idle/run very rich.

 
 
 
 

Thank you Texas for the link ! I do have everything up to spec (valve, ignition, airbox, carb boots) so the last thing would be to rejet.

Scirocco, not sure if you are asking me or LenB but I do have the plugs on the pilot jet port on both carbs so no problem on that end. And my plugs at idle look pretty good (to my understanding, after reading the KZ440 service manual, the pilot jet circuit is for idle). I only have this lack of power as soon as I open the throttle more than 3/4 (again, from what I read in the manual, it looks like the main jets need to be adjusted). If I remember well, you are in Germany no ? Would you have a website in Europe to recommend where I can find genuine Keihin jets ?

Sorry,only have a website for Keyster jets and rebuild kits for Keihin carburetor.

www.motorradbay.de/keysterjetsforkeihinc...ff9a2c1a271cdf8d057d

That's great thank you ! I will update once I have done the jetting.

Now do you want to know the easy way to rejet a KZ440 with CV36s?
Get a DynoJet jet kit for a 1981 KZ750H. You will have enough to do 4 carbs.
The KZ750H CV34s are the same as the KZ440 CV36s except for the carb body, which the difference is in the ventri size.
Jets, slides, needles, floats, etc... all interchange.
And if a different main is needed from what the kit supplies that is no problem.
On my ZRX i had to lean down my main one size.


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Hi Nebr_Rex,

Thank you for the suggestion. Correct me if I am wrong (since I have no experience rejetting carbs) but from what I read on the DynoJet parts description for KZ750 H 1981, the main jets they provide are size 116 to 136. This is way to big, knowing that I am trying to go leaner and that my main jet is 85 right now.

Why would it be easier then to use this kit ? I imagine the venturi size must be the explanation but I don't know enough about that. Could you explain it to me ?

I actually have a kz 750 H ltd, 1981, so could I try and use two of its carb on my kz440 (with kz400 engine) ?
 

Found out today that the #85 keihin jets I have had been drilled by the PO.
I had two spare #90 main jets and I decided to compare them to the #85 installed on the carb. The #85 are actually the size of the #130 I have on my kz 750 so the PO must have drilled them.
I put the #90 on the bike and it ran completely lean.
So I guess that I need jets in the 110-125 range.

Genuine Mikuni carb jets, Genuine Keihin carb jets and DynoJet jets are numbered different for the same size orifice.
Do not try to mix Mikuni and Keihin jets, the threads are often different.
DynoJet jets will fit the carbs they are  for. There are conversion charts posted all over the net for DynoJet/Mikuni/Keihin.


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