TOPIC:

Guys
I'm in need of a spec for the above if anyone can help please, I bought some VM30s from speedmotoco that should be jetted to the bike but it wont run at anything above idle so I think I'll need to start again. I've done all the usual points, condenser timing etc but it makes no difference. Perhaps they just sent me carbs with factory settings??? I'm really really pi$$ed. frustrated after spending all that money.

What, exactly, is it doing? When you turn the throttle, does it die?, Just bog down? Rune raggedy? Increase rpm or not?
Why VM 30s? That seems a little large for a 400. The 1000 came with VM 26 or 28. The VM 29 was a high performance option for them.

It just dies as if it was switched off, close the throttle and it picks up. 30's were recommended by speedmotoco and other suppliers.

Does the bike have the airbox installed? Ed

If the carbs were set up for an air box, they will not work properly with pod filters or velocity stacks.
Based on yor description, two things could be happening.
1. When you open the throttle, you are getting e severely lean mixture. This could be caused by low fuel level in the bowls, a terribly small main jet, or a needle setting that is much too low coupled wit a too small jet. Ther could also be serious manifold leaks or a combination of these.

2. When you open the throttle, you get a ferociously rich mixture. Much too large main jet and or needles way too high.

3. The carbs are way too big and there is not enough velocity with the throttle open to pull any fuel into the engine.

Yes, I said two. I lied.

Thanks Tex
Speedmotoco told me they were jetted to the bike and they supplied the pods and cable so they knew the set up. I was told they were a straight bolt on, you can see their adverts on ebay if you search kz400 carbs. Pulling the choke makes no difference so I assume its way too rich above idle.

Was the bike running before the new carbs were installed? If not, there could be other problems like valve lash way out of spec.

Are you running an open exhaust? If so, how short and did you discuss that with speedmoto?

I bought it without carbs so bought the mikunis thinking they were a bolt on replacement which is what SMC said they were. . I am very experienced with jap bikes and have checked everything else, valves are in spec and it ticks over very sweetly. I've tried both open and restrictive silencers, there was no difference. I've asked speedmoto what spec they think the carbs should be and I'll strip them to check. Maybe I'll get a std pair of kiehins to try..

Thinking about it, I told SMC that its a 75 KZ400D, with a stock set up and I live in the UK, I was expecting some questions but the next day I had email to say they had been dispatched, so I'm not sure what they have done, I have asked them.

For those unfamiliar I believe this is the kit he is referring to. www.speedmotoco.com/mobile/Product.aspx?...Code=kz400.30.mikuni

When I was looking carbs for my 440, I thought about trying these but didn't for a couple of reasons.

1. They claim they are "bolt on and rip"...yet different altitudes will require different setting according to the Mikuni tuning guide.

2. It seems as if they are saying the 400 and 440 jetting is the same. I know they are similar but I wouldn't slap a set of 400 carbs on my 440 and expect it to work.

3. They never state what the actual jetting is. Then that smug line at the end of the ad just pissed me off.

The stock VM30 is set up with the following

Bore Size: 30mm 
Spigot Mount: 40mm 
Main Jet: 250 
Pilot Jet: 40 
Needle Jet: P-5 
Throttle Valve: 2.5 
Jet Needle: 6F5 
Air Jet: 2 
Mikuni Part#: VM30-83 

It would be really interesting to see what you have in yours.

You might check out dime city cycles. They have a set up VM30 for the 400 and 440 as well. They clearly state what the jetting is and that it is a base line and adjustments might be needed.

I used it as a base line with my single carb kz440.



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Dom thanks for the reply, yes that is the kit, $400 to fit and rip......... Thanks for posting the "stock" set up, I will strip mine and reports back.

I've found the dime city spec now thanks and will go to that set up if I don't hear from Speedmoto.

This is what I'm using on my 76 KZ400 with MAC slipon mufflers and K&N filters.

Main Jet: #230,
pilot jet: VM22/210 #25,
Throttle valve cutaway (slide): 2.5
jet needle: #6F5 on #4, (STOCK Needle, 1 Clip Richer)
Air Screw: 1.75 turns out
needle jet: #159 P-5, (STOCK)
air jet: BS30/97 2.0, (STOCK)
needle valve set: VM34/39 3.3, (STOCK)
float height: 22-24mm (STOCK)

I started with a pair of stock setup VM30s. It was close but the pilot was way too big. A 30 pilot is too rich for me. The 25 is pretty good. I'd like to try a 22.5 because I think I'm just a hair rich on startup at idle. I think the 140 Main jets that Dime City spec are too lean, but they are running a different (richer) slide cutaway. I'm running the stock 2.5, I've tried a 3.0 but my bike did not like it. I have not tried the 2.0 slide that DIme City specs. Dime City is located in Florida so their elevation is about sea level. I live/ride at about 700 feet above sea level.

Thanks for your info. I've heard back from Speedmoto, the carbs as supplied have a 210 main jet. When I described the symptoms, they said simply that the main jet is too small and offered to send others to try. I think maybe Dime are jetted with stock airbox as mine wont run with 210 and pods. I will post the full spec when its to hand.