KZ440 Single Carb Conversion

I did a lot of research from many different forums to get information on this project so I figured I would share my work with you all.

Like many other KZ owners, I worked with the CV carbs for many hours to get pod filters dialed in. The end result was still fairly dull and slow so I wanted to improve my bike as much as I could. I started researching single carb conversions and found that most people used an older CR carb or Mikuni VM series round slide carb. I could pick up a CR carb for ~$50 on ebay or my local salvage yard or get a brand new Mikuni on amazon or ebay for $80.

I went with a new Mikuni VM34.


Next was figuring out how to make the manifold. I decided on using 1.375" x 2.5" radius, 180 degree mandrel bent tube from Columbia River Mandrel found here

Tubing and flanges




For the flanges, I used 1/4" x 2" flat bar. I bored the center hole 1.25" with a mag drill and then laid out the bolt holes and shape cuts based on the dimensions of the old carb boots.

Next was getting the tubing centerline to fit the intake holes. I cut the legs off the hoop as close as I could and then had to cut a section out of the middle to make the centerline dimension correct.

I forgot to take a picture of the center cut but I ended up taking about 3/4" out of the middle of the hoop and then welded up the center seam.

I then made a jig from a piece of angle iron to bolt the flanges to and weld up the whole thing. The center hole was done roughly with a grinder and air sander. The short center piece to fit between the carb boot flange and the manifold was done the same way.


After fully welding it up, I fit it to the bike to see how it worked. My measurements worked perfectly because the throttle cable coming out the top of the carb fit right up through the small gap between the frame tank tube and the seat frame.




I had to use a wirefeed welder because my tig was down during this project. For any manifolds I do after this, everything will be tig'd.

Pod filter options for VM34 come down to K&N, Mikes XS or UNI. I picked up a UNI for $17 on Amazon.


All finished and running


For Jetting, I went with a #35 Pilot jet (it came with a 25), and a 170 main. It came with a 260 main but I purchased several jets ranging from 160-200. I knew a 260 would be too big.

For a throttle cable, my local motorcycle shop had a cable for a 70's honda CB/CL175 that was the correct length. It's almost perfect but the cable is just short maybe 1/4". I had to take the jam nut off the top of the carburetor adjustment to make it work correctly. Modifying the stock cable to fit the VM might be a better option for some.

Throttle response with the VM is incredible. It feels like an old dirt bike now. I was starting to get used to the fairly dull feel of the CV carbs but I am extremely happy with the new setup.

My bike with the old carbs


It's getting stripped down and everything is getting powder coated in a few weeks.

nice job :evil: .

thanks for the tutorial,i am sure it will help many folks in the future.

cool lookin bike also.

make sure and post some pics up after pc.

leon

Nicely done!
Wayne

Excellent work! Bike looks great!

Thanks guys. Here's a couple more pictures of my bike.

My shop and shop mate's 240Z





Battery box and wires tucked under the seat

Very clean install, nice looking ride.

Wow, awesome job. I love this bike :woohoo:

Very nice work.

BTW, nice 240z. I had Z cars for many years. One trick that made the car way easier to live with, was to put a 90 degree bend in the tailpipe, and shoot the exhaust out the side. This greatly reduces the exhaust from creeping in the windows. The farther out he can get it, the better. I usually cut the pipe almost even with the bumper.

If you don't, I think the shap of the car pulls exhaust along the side and it gets in the window if you have the window open.

loudhvx wrote: Very nice work.

BTW, nice 240z. I had Z cars for many years. One trick that made the car way easier to live with, was to put a 90 degree bend in the tailpipe, and shoot the exhaust out the side. This greatly reduces the exhaust from creeping in the windows. The farther out he can get it, the better. I usually cut the pipe almost even with the bumper.

If you don't, I think the shap of the car pulls exhaust along the side and it gets in the window if you have the window open.

We're in the process of building a new L28 for it right now. I know it does smell like exhaust all the time inside so I'll pass on that advice to him.

Nice work man! Apparently you and I have similar taste. My 400 is styled almost identically. It has clip-on's in my pictures on this forum, but I just replaced them with riser bars.

I am also running a 2-1 with the VM34. Although I am still dialing it in a bit, it sure beats the hell out of those old CV's!

Barreto,

Thanks for the write up. It's one of the better ones I've seen for a 2-1 manifold. I'm thinking about doing the same thing for my KZ750 & will be using this as a template. Could you provide some dimensions on the manifold? Distance between pipe (where it meets the engine, not sure of correct terms), I would like to compair it to the 750. Thanks again for sharing your info.

I've seen this done with pvc piping too. This is much cleaner.