HELP NEEDED KZ400

sorry... dupe posting

Post edited by: wiredgeorge, at: 2007/07/27 13:32

I believed this was common knowledge:

The CV series carburettors equivalent size is smaller than the venturi area. A 30 mm CV carb probably has the same venturi size as a 26 mm round slide Mikuni.


The 1974-1976 KZ400 D and S, and the 1977 KZ400A all had Keihin CVB36 carbs. (Yes there is a misprint on page 5 in the Kawasaki workshop manual. In the carb chapter they are refereed to as CVCB36.)
The 1977 D4 and S3, and the 1978 A2, got Keihin VB32 carbs (with rubber diaphragms).

And the different jet sizes and jet needles and needle jets used are more than just numbers. They are a result of several factors, some as a result of trial and error from the Kawasaki factory, and some as a result of differences in the engine compression, and some as a result of changes made to the air filter system and the mufflers between the different year models, and which country they were purchased to.

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Post edited by: ibsen22000, at: 2007/07/27 14:22

Also, I'm pretty sure the S2 used smaller main jets than the D3 (1976). The 76 S2 model has a more restrictive 2-into-1 exhaust. I believe the main is 125. At least that is what was in the 76 S2 carbs I had, and I think I confirmed it with Ivar a long time ago.

Kawasaki.com shows the 75 S uses 125 main, but the 76 S2 uses 130 main. However several different jets are shown as options, so basically it's unclear.

It really doesn't make sense. The 75 S is listed as 125 main, but dual exhaust. While the 76 S2 is listed as 130 main and single exhaust. It should be the other way around... 75 S with 130 main, and 76 S2 with 125 main (which is what I actually found in the actual carbs).

It may just be too unreliable to use documentation from Kawasaki manuals and fiches from that era.

Post edited by: loudhvx, at: 2007/07/27 15:45

SO is the misprint the 32 even though the carbs measure 32?

Post edited by: loudhvx, at: 2007/07/27 14:52

loudhvx wrote:

SO is the misprint the 32 even though the carbs measure 32? Is it possible the same slides were used on 32's and 36's and that's why the slides have a 36 marking, even though they are installed in a 32mm carb?

Read this again:

"The CV series carburettors equivalent size is smaller than the venturi area. A 30 mm CV carb probably has the same venturi size as a 26 mm round slide Mikuni."

The 36mm CV carbs have got an actual venturi area of 32mm. The 32mm CV carbs venturi area are probably 28~29mm.

And on page 103 in the manual they list the jet sizes for the CVB36mm, while the jets for the CVB32mm are listed on page 196.

I got ya, so the newer carbs actually have smaller diameter than the older carbs, then? That's unexpected.

Oh well, time to edit the manual.

So is it the CV's that have the naming discrepancy or is it the whole Keihin brand that is like that?

I guess I should edit these posts to prevent further confusion.

No, all other Keihin carbs; ae CV40, CV34, CVK36, etc measure the actual venturi size. The CV40 is used on the Harley big twin and measures about 40.5mm ID, the CV34 used on some of the 4 cylinder KZ750 models is about 34.4mm ID and the CVK36 used on the Vulcan twin carb VN1500A/B/C is just a shade over 36mm ID. The CVK32 carbs on my Voyager XII are 32.4mm or so... the nomenclature for the CVB36 seems to be something of an anomoly. Not sure what to tell you.

Oh yeah, the Mikuni BS series carbs are all about .5mm over their named size... BS34 is about 34.4mm and BS32 is about 32.5mm if memory serves.

I'm sure that is correct also as most producers at one point started to use the exit diameter of the carb for sizing, and not the venturi area diameter.
But some tuners prefer to use the venturi area size as this is where peak velocity occurs and where fuel is added to the air.

As an example; the 40mm Keihin CV carb have got a venturi area of 46.5mm/1.851" and an exit diameter of 40mm/1.590".

And the Keihin CVB36 used on the early KZ400 are sized in venturi area diameter.

Good info! Ivar, Please pick apart the sheet on carb specs I posted... as time goes by, I will try to fill out the information better as some of the info isn't really coming off the carburetors themselves but is what I found published and I have found that there are different jet needles used than are listed and different ID marks as well... The main difference visually between the 74/75 carbs and 76 carbs is the slide... one is dished in the cut out area and the other is square.

I believe the 400 is the most complicated bike to tune and keep running. I wish it was FI.