Mikuni vs Keihin pod filter rejetting KZ400

Hello guys,
I just want to know what do you guys think.
Is the Mikuni vm30 better for air pod filters or is the Keihin for air pod filters?
I currently have the stock Keihin on my kz400 and I need to rejet them to my pod filters. Or should I get the Mikuni vm30s that is already pre-jetted from this website:
www.speedmotoco.com/kz400-kz440-vm30-mik.../kz400.30.mikuni.htm

The Mikunis are easier for the beginner to get jetted right.
Do not count on the carbs to be jetted right. 30s are to big
for a relatively stock 400cc engine. 28s would be better
and 26s would be best.


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What size jets do you use? Also is $400 expensive for the Mikuni carbs?

Another member recently used the carbs from speedmotoco.
See kzrider.com/forum/3-carburetor/603345-kz...-jetting-spec#735946

Not sure if he resolved the issues

Try using the search function here.

FWIW, I put VM32s on my relatively stock '74 KZ400 cafe racer and they are perfect. It has very mild porting, UNI pods and lengthened exhaust with EMGO chrome cheapies out back. The bike runs like a dream, idles smoothly and pulls hard. The VM carbs are head and shoulders above the stock vacuum CV carbs. Anything smaller than a VM30 and you might as well stick with the CVs. A performance article on the KZ400 from back in the day called for swapping out the stockers for VM32s. That article is somewhere on KZ400.com if you have a look around.

$400 is way too much. "Pre-jetted" is just code for "Pay me more money for these because you'll never be able to jet them yourself", which of course is bull. Jetting is very easy once you have a couple of tunes under your belt.

I got my VM32s for right around $95 each shipped plus another $35 for the 2-into-1 cable. While tuning them, I had to go with 2.0 slides for another $25 per, but we sold off the 3.0 slides for $20 each to almost offset the cost. If you do go with the VMs, Just make sure you buy one that has LEFT side idle adjust and one that has RIGHT side idle adjust.

Here are my specs if you're interested:
1974 KZ400
Standard Bore, Stock Cam, Stock Ignition, Very Mild Porting & Smoothing
NGK B8ES Spark Plugs Gapped .030”
93 Octane Sunoco Fuel
Timing and valve clearances set to FSM specs.
Carbs: Mikuni VM32
20 Pilot Jets
210 Main Jets
2.0 Slide Valves (The 3.0 slides that came with the carbs gave it a “lean stumble” at 1/8 throttle. The 2.0 slides cleaned that right up.)
6DP17 Needles, Center Clip Position
23mm Float Height
Air/Fuel Mixture Screw – 1.75 Turns Out From Lightly Seated
UNI Pod Filters (lightly oiled)

WOW thanks!!! Also another question KZCafeChick, do you have stock mufflers?

kyan44 wrote: WOW thanks!!! Also another question KZCafeChick, do you have stock mufflers?

You're welcome. No, I have Emgo reverse cone mufflers. :blush: You can see my bike in the projects section. The thread is titled 1974 KZ400 Cafe Racer Build".

Cancel what I said about 210 main jets. I pulled the plugs and they were showing a moderately lean condition, which I already knew before reading the plugs. I swapped in a pair of 220s and it was much better, but I think it's going to want 230s in the end. I'm not sure if that's because of the mild porting work I did or what, but I'm surprised it wants so much fuel, even with it having 32mm carbs that are pulling some serious air.

If I were in your shoes, I'd put the stock CVs up on ebay and invest the $100 or so that you can get for them into the VM32s, 2-into-1 cable, 2.0 slides, UNI pods and the jets I mentioned. And open up that exhaust. Even the cheapie Emgos that I'm using right now flow a lot better than the big stockers.

Those are some awfully big jets. Have you looked at what KZ900/1000s are using.
The carbs are set up for 2 strokes and people are using them on 4 strokes. You should
consider going a step further on the slide. Heck my GPz1100 with RS34s has 140s.


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Nebr_Rex wrote: Those are some awfully big jets. Have you looked at what KZ900/1000s are using.
The carbs are set up for 2 strokes and people are using them on 4 strokes. You should
consider going a step further on the slide. Heck my GPz1100 with RS34s has 140s.
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I considered a 1.5 slide, but I'm pretty sure that would make it too rich off idle. Then I'd have a "burble" instead of "stumble". lol I have neither with the 2.0s and I can whack the throttle as fast as I can from idle and the motor keeps up, so the slide size is spot on.

RS34s are completely different carbs from VMs. And the difference between the 900-4 and a 400-twin is only 25ccs per cylinder, As you know, carburetion is per cylinder, not based on the motor's displacement as a whole. (Not saying that in a bad or condescending way, just putting it out there for the other folks who are new to carb tuning.)

Since 32s flow a lot of air, they need a lot of fuel. If one's purpose is to make the motor reach its full potential, especially a high RPM (for a twin) motor like the 400, you need to get maximum air and maximum fuel into it. 26s, 28s and even 30s just don't do that, so it's perplexing why everyone is selling 30mm carbs as the hot ticket for a 400. 26s are way too small for the 400 and should never even be considered. 28s are about as good as using the crummy stock CVs, 30s are a lot better, and they'll work fine, but still won't maximize the engine's potential.

All I know is that the 32s are absolutely perfect on my 400 for what I want it to do, which is be as powerful as it can be. The 32s took a mundane little commuter bike and made it quite quick. And not just on the top end when the motor is howling. It's also markedly better right off idle. I would almost go as far as to say that I'd put my 400 up against my stock 650sr and they'd be extremely close. Granted, my 400 weighs about 160 lbs less, but that barely makes up for the 250cc displacement discrepancy.

As for my jet sizes, I was lying in bed last night thinking that even the 230 mains might not be enough. It may want 240s. Yes, I know that's getting big, but the motor wants what the motor wants. I'm starting to think that my porting work did a lot more than I was expecting. Short of dyno testing, the plugs, seat of my pants, and my engine tuning experience tell the tale. Since I'm getting so close on the mains, it's just about time for a couple of plug chops.

By the way, for the O.P. Kyan, whatever you do, stay away from the Emgo pods. UNI or K&N is the way to go. Years ago I cheaped out and put Emgo pods on a bike and it ran like hot garbage from the low-mid on up. With the same tune in the carb, I switched to UNI pods and it was night and day better.

Thanks! I am thinking about keeping my stock carbs with uni pod filters. What do you think? KZCafeChick?

kyan44 wrote: Thanks! I am thinking about keeping my stock carbs with uni pod filters. What do you think? KZCafeChick?

The stock CVs with pods are difficult to tune, but not impossible. You'll never get the same kind of power and throttle response out of the CVs that you will with the VMs.

Bear with me on this. A couple years ago, a neighbor of ours a few houses down asked us to "lightly cafe" a '75 CB500 Twin he had picked up. (It had the crummy CV carbs on it from the factory also) No frame cutting or anything spectacular, just stripping the bike down, repainting, making some styling changes, doing up a traditional cafe style seat and getting it running correctly. He was on a budget, but we kept telling him to go for a set of VM34s. He kept saying he'd love to, but would rather put that money into styling type stuff. Well, we finished the bike, he was thrilled with it, but started asking if the VMs would make that much of a difference, so of course I told him "heck yeah!". He finally broke down and bought them and had me put them on and set them up. After giving the bike back to him, every time I saw him for the next week he would thank me for suggesting the VMs. They really do make a huge difference.