New guy KZ400 project.

Hey everybody.. my name is Jeremy. I picked up a 1978 kz400 c1 a couple months back and have fell in love with this thing. I'm looking into getting into vintage road racing.(AHRMA,WERA,ect.) Hopefully I can pick some your brains for information on racing and getting this bike setup. Here she is as of now...


I do not have any pictures handy from when i purchased it. but here was the aftermath of night one..



this was just getting the bike into riding condition. (it was running and riding when i purchased it but it wasnt safe)

here she is as she sits today.. (the bike was completely stock and original when purchased.













let me know what you guys think.. just the basic tune up made a huge difference on the performance.

I then added pod filters and replaced the factory muffler with a cheap muffler i found at a used harley shop. Then we rejetted the carb and this thing runs a lot better then expected. My buddy on a 2013 ninja 300 was impressed with the torque. he could really only pull me on top end. and this thing runs all over ninja 250's. I can't wait to get the suspension sorted and get this thing on the track.

Looks awesome! Where'd you put the battery, in the tail?

yea it has the smallest conventional battery in the tail. i used to pieces of angle iron and welded them across the rear tubes and put a strap on it. The regulator/rectifier, and the fuse box is all back there. Its worked out great.

I've debated running one the extremely small ballistic 12v batteries, but now that im planning on tracking the bike.. i may need to keep a bigger battery so that I can remove the alternator during races. but this just depends on the class i am in.

Looks like your off to a great start.
Have the steering stem bearings been replaced with roller bearings yet?
When you decide to switch to slide carbs or want to get some more power out the ol' twin p.m. me.
I have 2 that I've been tinkering with for a few years now.

I would love to pick your brain on these little 400 motors. I've read some build threads that have inspired me to stick with this little guy. Right now my motor build is looking like its going to be:

decked head and block (for compression increase)
port head
webs cam
valve springs (supposedly rd400 valve springs work great)
adjustable cam gear
and build a nice 2-1 exhaust
and get rid of these horrid diaphragm carbs

You have the late 400 which is just a small bore 440.
Decking the head .035 and removing the base gasket (use 1194 for a sealer) will raise your compression from 9.5 to 10.7.
That will also retard the cam 10 degrees,advance it 1 tooth will place it 5 degrees advanced from stock.
There are no off the shelf cams,with a milled head you will have to check piston to valve clearence.
On the 440 there is plenty of room,but the 400 has a taller piston dome.
Ports and valves are already large enough for a cylinder 50cc larger,just smooth the sharp edges.
Mac makes a 2 into 1.
All gaskets and seals are available except the clutch push rod seal.
I think I seen where some rig up something using a different seal for it.
For vm28 Mikuni carbs use the universal off road Mikuni carb boots.

Being a mechanical engineering student i have complete access to an extremely nice machine shop. so making an adjustable cam gear isnt a big deal. hell i made a set for a Nissan KA24DE pretty easy on my last car motor build. For the cam.. I have read that webscamshaft use to produce a kz400 cam. They still have a couple of cam profile specs for the couple cams they have made. They are the company that mentioned using RD400 valve springs with their cam. I'll get more info on it soon. After i get a decent pair of shocks for my bike, acquiring parts for my motor build will be next. I really need to get my hands on another motor with a 6speed trans for the build. I'ld like to save my motor for a reliable back up. (it only has 7k original miles on it)

Very nice job! I used to have an S13 too. Really miss it.

Yea I love my s13 but its down at the moment awaiting a rebuild. Its been a drift car its whole life. Now its getting an itb'd vh45 and slowly transforming into a time attack/hill climb car. Its going be a long project. I'm going to make it my school project. So basically build the car as I get farther down the path of my engineering major. So that I can apply the knowledge learned in school. Plus the project I make in the machine shop can be part for the car instead of random crap.

Web used to grind cams for the early 400 (4 bearing journals)
Your bike has the late 400 (3 bearing journals), same head and cam as the 440.
If you get them to grid some late model cams let me know,I'd be interested in a few.
And since yours is a late 400 it should have a 6 speed.

^^ my bike is the odd 78 c1 its a drum brake, kick start only, came with only speedo (no tach). and has a 5 speed. apparently its an odd one.

I will have to contact web about a later kz cam then. i feel like the motor i read about with the webs cam was a later kz motor.

this is one of the builds i was refering to.. its strangly fast. almost makes you want to question its credibility.

www.armbell.com/forum/viewtopic.php?t=12394&mforum=kz400