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1976 KZ400 jetting w/ pod filters 12 Apr 2017 20:46 #759070

  • alinaaseh
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Hi folks.

I have a 1976 KZ400. Keihin VB32 carbs w/ pod filters, #125 main jet and #35 pilot jet. Bike was a non-runner when received from previous owner.

Bike starts on first kick with choke engaged. When in neutral, it revs smoothly and freely with choke engaged. If choke is disengaged while cold, bike dies immediately (which is assume is normal). If choke is disengaged after several minutes of warming up, bike will idle at a very low RPM for several seconds, sputter, and die. Bike will also die whenever clutch is engaged from a standstill, no matter how much gas is given. If clutch is engaged after a rolling start down the driveway, the bike will cruise around the block, but is severely underpowered.

A quick look at the manual reveals that these are all signs of a LEAN fuel mixture, most likely because the previous owner removed the stock airbox and installed pod filters. I assume that I must increase the amount of fuel by sizing up my jets in order to get the bike running properly.

All this being said, my questions are as follows:

1) Partzilla only shows one size available for the pilot jet: #35. Should this jet remain as is?
2) If so, should I increase the size of the main jet from #125 (current) to #130 (standard stock jetting, according to manual)?
3) Should I go HIGHER than #130?
4) If so, in what increments? The only main jets above #130 are #135, #140, #150, and #160.
5) Will increasing the size of the main jet solve all my problems?
6) If not, will I have to adjust the needle, or some other magical carburetor part that I've never heard of?

Best,
A
1976 KZ400 D3
Ft. Collins, CO

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1976 KZ400 jetting w/ pod filters 13 Apr 2017 06:19 #759093

  • diggerdanh
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Welcome, I have a 76 KZ400 too, which was my first bike and my first project and started me down this journey.

Yes, it will die if choke is disengaged too early. The KZ400s are known for being cold-blooded and are a little difficult to get started cold and need to warm up a bit before the choke can come off completely. When bringing it out of a deep slumber or when it is chilly outside I sometimes have to fiddle with the choke and throttle for a bit to keep everything on track.

Don't let that bike run at very low RPM - it should be setup to idle at 1000-1100 RPM. Much lower than that and you may risk not getting enough oil to the top end and running into issues.

If you are not dead set on running pod filters then I would consider buying an airbox and carb to airbox boots from Ebay or someone parting a bike out locally. The CV carbs were designed to run with an airbox that provides lots of stable air. The bike with the stock carbs will run best with the airbox and you'll likely not need to make any jetting changes to the carbs at all. The stock carb and airbox setup is very forgiving and will work in a variety of environments and scenarios.

As I'm sure you know the carbs on the early KZ400s, 74 through some 77s, use a piston rather than a rubber diaphragm so the good news is that you don't need to worry about checking for pinholes and replacing that diaphragm. But that piston needs to ride inside that carb bore really well. Make sure it does - check for any burrs or anything stopping it from doing so. I am now running Mikuni VM30s with K&N filters but when I did have the stock carbs cleaned and dialed in they ran really well.

If you are set on running pod filters with the stock carbs, well... it can be done but it is not a simple task. You will have to invest some time tuning to get it working well:

What type of pod filters are installed? If it is a cheap pair of Emgo or generic filters and you are set on using pods then I would buy a pair of K&N or Uni filters. The cheap filters have a rubber lip in them that are said to block the air bleeds in the carb opening. I have read of people trimming down that lip but I'd rather spend the extra few dollars on better filters.

It sounds like the primary issue you are having is on the idle and part-throttle side, which is not something that a main jet change will fix. The main jet is really mostly in play at half throttle to full. That doesn't mean the main jet does not need to be changed, it probably does, but focus on the idle and part throttle issue first.

You may not have much luck getting jets from Partzilla and other like places, especially not pilot jets. The carbs are Keihins and takes Keihin jets, so you just need to figure out which ones. At one point I determined which Keihin jets were the main jets for those carbs but I've lost my notes. If you pull a main jet and a pilot jet you should be able to measure them and determine what type they are. These links can help identify them:
www.pjmotorsports.com/keihin-jets.html#main jets
www.pjmotorsports.com/keihin-jets.html#pilot/slow jets

Once you figure out what type they are you can put those numbers into a Google search and find several places, power-barn.com is where I have bought them before, that sell them for a good price. I would buy each of a couple sizes up for both the main and pilot jets. Then you can start experimenting. Make one change at a time, starting with the pilot jets first. Start with the idle circuit. Go up a pilot jet, adjust the air/fuel screw until you get best idle, check the plugs. If it is still too lean then go up another size. Rinse and repeat. You'll need a lot of plugs.

Then work on the main jets,

For tuning the midrange, the needles do not have clips to be able to adjust them. However you can use very small washers to raise the needle a bit at a time and see id that helps.

Best of luck. Keep us updated.
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Last edit: by diggerdanh.

1976 KZ400 jetting w/ pod filters 13 Apr 2017 06:35 #759095

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I looked through my old order confirmation emails and I believe that the main jets for the keihin piston-style CV carbs are these Keihin 99202-601-XXX Press Fit Type Secondary Main Jets:
www.power-barn.com/keihin-99202-601-xxx-...secondary-main-jets/

And the PJ Motorsports page that I linked to in the previous post lists them as fitting Kawasaki KZ400 D/S.

I checked my notes and I was using #135 main jets with stock airbox and aftermarket exhaust and it ran well.

Now you just need to pull a pilot jet out and measure it and determine what style of Keihin jet it is. Please post your results when you figure it out.
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1976 KZ400 jetting w/ pod filters 14 Apr 2017 22:33 #759208

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I've also come to the conclusion that the main jet for the carbs on our bikes is 99202-601-xxx. Good call on Power Barn - the price seems right and the descriptions are useful. I will start with #135 and see how it goes, but since I'm running pod filters, I'll get #140 just in case.

But, like you mentioned, I'll need to start with the pilot system first. I've pulled the pilot jet but I'm having an extraordinarily hard time identifying or finding it. It's marked #35 (which the manual says is stock), but can't for the life of me find one that looks like it AND goes all the way down to #35 on PJ Motorsports. Or Power Barn. Or Jets R Us. Or Partzilla. The only one I'm finding is the stock #35 on eBay (Kawasaki Part #92064-043). It looks similar to the Keihin Part #99101-124, but Power Barn lists this as an air jet.

How much trouble do you think I'd create if I changed the main jet before I change the pilot jet? I'll keep digging, but I don't feel confident that I'll find the correct one.
1976 KZ400 D3
Ft. Collins, CO

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1976 KZ400 jetting w/ pod filters 15 Apr 2017 09:19 #759230

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No eBay APP ID and/or Cert ID defined in Kunena configurationAfter reading your post and doing some searching I found some NOS #40 pilot jets listed on Ebay. I'll see if I can find it again.

Here you go:

It would not suprise me that the pilot jets be classified as an air jet by Keihin.
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1976 KZ400 jetting w/ pod filters 15 Apr 2017 10:31 #759232

  • alinaaseh
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Thanks, diggerdanh. You always seem to be a step ahead of me - I continued my search for several hours after that post, and stumbled upon the exact same ebay listing. They seem to be the only #40 pilots for our carbs on sale.

Now, here's another question. The pilot circuit takes the following route, according to the manual: float bowl -> main jet -> pilot jet -> slow jet -> etc etc. The slow jet sits immediately above the pilot jet when assembled, and is also #35 from the factory. If I increase the size of the pilot jet from #35 to #40, should I do the same for the slow jet?

Ali
1976 KZ400 D3
Ft. Collins, CO

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1976 KZ400 jetting w/ pod filters 15 Apr 2017 15:55 #759244

  • loudhvx
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Be aware, with the piston slide CV's, the slides must be free to move very easily and consistently. Due to wear over the last 40 years, you have to sometimes play with the slide covers so the slides can move very freely. They need to be super clean, and then add about 1 drop of motor oil onto the sliding parts. That will usually make a big difference.

I have jetted a couple of those bikes and never found them to be very cold blooded. Usually, I find the choke can be removed in just a minute on a moderately warm day, like 60 to 70 deg F. The ones I worked on also had the air jets altered for pod filters, in addition to the fuel jets.

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1976 KZ400 jetting w/ pod filters 22 Apr 2017 23:00 #759984

  • alinaaseh
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diggerdanh & loudhvx:

Just received all my jets in the mail. I increased pilot and slow jets from #35 to #40, and increased main jets from #125 to #140. The bike is now harder to start, and won't idle at all, regardless of whether or not the choke is engaged. The bike is quite a bit more responsive when actually riding, but still underpowered. Also, anytime I pull the clutch or attempt to idle, the bike will die.
1976 KZ400 D3
Ft. Collins, CO

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1976 KZ400 jetting w/ pod filters 23 Apr 2017 06:43 #760000

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If anyone ever gets a KZ400/440 with pods to perform on par with the stock setup, please call Guinness. :lol:

Good Fortune! :)
1973 Z1
KZ900 LTD
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1976 KZ400 jetting w/ pod filters 23 Apr 2017 08:01 #760012

  • loudhvx
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The final setting we came up with on a 76 Kz400S2 with stock 2-into-1 exhaust with the muffler cut down was as follows, according to my notes from back then (10 years ago). We only had a crude ega gas analyzer back then... no wideband o2 setup yet:

6/20/07
drilled out main to 140.
drilled out slow jet to 37
Replaced bowl gaskets K&L KL18-2634
Replaced leaky main-jet orings 4.2mm x 1.1mm #4609 (see KZ400carbOrings.gif for oring details)
Now using:
Emgo disposable pods
#35 slow jets from a 1970 Honda CL350. (drilled out to #37. The emulsion holes are bigger.)
#35 pilot jets (drilled to #64)
#68 (89?) starter jets
#140 main jet (Drilled out the 100 Honda jet to 140)
#90 pilot air jets
#40 main air jets (drilled to #60, .6mm)
Set mixture screws 1 turn out.
Ega shows 13~13.25 at idle. but 12~12.5 off idle
Cut down exhaust


I don't know if the jet numbers are stamped in hundredths of millimeters or not, so I can't be sure if the air jets were drilled. So when I say "drilled out to xxx", that means I measured the orifice with a drill bit and converted that to hundredths of a millimeter.

For example, "#35 pilot jets (drilled to #64)" would mean the jet was stamped 35, but actually measured 0.64 mm.
Incidentally, we felt the 64 was probably way too big, but it wasn't a major issue since the pilot is stacked with the slow jet.


Also be sure you have the air jets in the right holes. It's easy to swap them accidentally. Here are my notes on that:

Pilot air jet: Small stubby screw-in type jet that goes in the top of the carb.
Main air jet: Small stubby screw-in type jet that goes in the top of the carb.
note: the main air jet has a smaller orifice than the pilot air jet.
From the top, the main air jet and pilot air jet can be swapped accidently.
The main air jet goes between the pilot air jet and the screw that holds the plate.



As you can see it was a real mish-mash of parts etc. The reason is some of it was already altered before we got to it. I think the final jeting would have been much simpler if we could have started with stock jetting. We had to use some honda jets which were slightly different, but I don't think the difference was significant. The previous owner over-drilled some of the jets so we used some extra honda parts we already had.

With this final setting the bike definitely seemed faster and smoother than the stock 400's we compared with. We also spent a lot of time getting the ignition working properly. We converted it to a point-triggered electronic module.

Through all of it, we never had difficulty getting the bike to start. It would start on a wimpy first kick almost every time. (Cold or hot, I think we may have not even used the choke on very hot days.) And that was even with a small scooter battery which was dead when we got it. It couldn't even power the headlight with the bike not running. But in one kick it would start and the headlight would be bright. We spent a lot of time on the electrical. Over the course of 3 years we rewired the whole bike, converted to electronic ignition, and made a custom solid-state regulator.

As I said earlier, the most important thing, for us, initially, was getting the slides to rise and drop in unison. If you tip the carbs upside down, you should only hear one click when the slides reach the top, and when you let them drop, you should only hear one click when they both hit bottom. If one is slower than the other, loosen the top cap and play with the slide up and down as you snug up the screws. That will let the cap tighten in the correct position to prevent binding.

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Last edit: by loudhvx.

1976 KZ400 jetting w/ pod filters 23 Apr 2017 08:05 #760015

  • Nebr_Rex
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Been there done that.:woohoo:
Check out page 12 in the link on the bottom of my sig..
2002 ZRX1200R
81 GPz1100
79 KZ1000st daily ride
79 KZ1000mk2 prodject
78 KZ650sr
78 KZ650b
81 KZ750e
80 KZ750ltd
77 KZ400/440 cafe project
76 KZ400/440 Fuel Injected

www.dotheton.com/forum/index.php?topic=39120.0


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Last edit: by Nebr_Rex.

1976 KZ400 jetting w/ pod filters 23 Apr 2017 08:20 #760018

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Nebr_Rex wrote: Been there done that.:woohoo:
Check out page 12 in the link on the bottom of my sig..


I get this when I check the link:

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