Hi!

I recently finished restoring a ‘76 Kawasaki KZ400.
I did a extensive rebuild, except for the engine: I changed wheel bearings, cleaned the carbs, electrics, new sprokets, new plugs, new coil…

Kept it mostly stock, except for the air filter which has been swaped for a pair of K&N filter pods.
 
Carbs have been throughly cleaned and properly sync, cam tension is correct, so is the ignition timing, valve lash is within spec, compression is perhaps a bit on the lower side (last time I checked was 125 and 115 PSI cold) but within spec nevertheless. Carb vacuum is perhaps a little low (20 cm Hg) (manual states 22-27 but then again I’m using some cheap gauges). Charging system is good as well.

The bike has stable idle and has plenty of power. Had a look at the spark plugs after some miles and the bike appears running just correct, not reach or lean (typical pod problems).

I also checked the engine mounts, fork, swing arm and every single bolt on the bike and everything is properly torqued.

The problem I’m having is that I’m getting HUGE vibrations that come and go with no apparent reason. These vibrations don’t seem to be rpm, gear, temperature or speed dependant. They just appear and disappear randomly.

I may be cruising nicely, holding the engine at stable rpm and out of nowhere the bike may start to shake like hell. To the point that my hands and ass go numb and the bike is barely rideable.
Then, after some miles, all of a sudden, the vibrations may disappear and the bike start to run so smoothly that you would’t tell whether the engine is even running or not. As if you were riding a bicycle.

The bike normally runs a little rough compared to the smoothest state, but not as bad as the shaky state. It keeps giving power nevertheless.

This also happens at idle, sometimes it’s shaky, sometimes remains super smooth.
There are times that the bike cold cranks smooth, and others not.

I have tested whether the bike is running on one cylinder when this rattle happens, unplugging a spark plug cap
at a time, but both of the cylinders seem to be working.

I’m a little bit confused because if it was an engine balance problem or compression related, the vibration shouldn’t come and go, right?
The same if it was an ignition timing problem, or any electric problem.

My only guess is that it can have something to do with the carburetors, which are not delivering a contant mix of fuel and air but I have inspected and cleaned them twice.
In addition, what could be causing this random behaviour?

Any ideas?? 



 

This is a ongoing project bike I first rebuilt in 2012. I bought the complete bike in bits for $200 and it has been my main street bike until 2021 when I removed the engine. The frame has now been converted to run a Z1 engine.





Its a early '77 B1 frame that has been converted to use '81 GPZ550 wheels/brakes/fork/swing arm. I bought it this way, it came with a '82 CSR engine, and it had been road raced at one point (drilled/wired)

The first 650 I bought in 1984 had been rebuilt by me right after I bought it. I built that engine up with a new 831cc MTC piston kit, self ported and modified big valve head, and GSXR750R flat slide carbs bored to 33mm.



This same bike went on to be drag raced after I stopped street riding in 1992.



The engine was retired in 1996 but the chassis is still a race bike. This original 831cc engine is what is in this street bike build (cases/pistons) The pistons were originally 13:1 but were cut down to around 11:1 compression. A new barrel was built with oversized liners.



A new 650 street head was built using 35/31 SS valves sunk back and ported to flow as much as a GPZ1100. Actual measured compression with this head is 9.9:1



Cams are .400" lift WebCam #189, and carbs vary from VM26 to RS34's. In sleeper mode it probably makes around 85 HP to the wheel, more with pipe/pods.





For most of its life it was running a MAC 4 into 2 megaphone exhaust and a air box (sleeper mode) but on occasion it has had a pipe and pods.



Currently the engine is together and sitting on a cart waiting till I get another frame built for it.

The ZX9-R parts are the right choise, only the swingarm could be a problem to your conversion.
I bought a cheap ZX9-R donor bike and use the K&J swimgarm to get street legal in my built.
Got a steal deal on a GSXR 1100 mono shock, engine and mounting kit for the Z1 frame.
I did a pre-test fitment of the parts but i don´t have the time to do the full conversion.
Let´s the pics talk........

 

There are a lot of custom sport bikes with extended swingarms, but I don't have a clue where those are made. My guess is that they are custom, and I'd probably look around for custom bike shops that do fabrication.

The early '80s GS1100 swingarm is a bolt on swap for the KZ900/1000 frame.  It's aluminum, and longer than the KZ arm.  But I don't have any idea if it will fit the wheel you have in mind.  The stock wheels were definitely not that wide at the time.

No matter what you do, you're likely going to need to do some fabrication.  Rear wheel size is not the only variable.  There are tons of different axles sizes, axle spacers, and brake mounting setups. 

The one place I know of that does really cool looking custom swingarms and other bits is Patriot Racing (formerly Motogpwerks).  They purchased the rights to CalFab, and have been making modern recreations of period CalFab swingarms.  My guess is that if you have the budget, they might be willing to make a custom setup for you.

patriotracingindustries.com/calfab/?page=3

I was planning on swapping out my swing arm. 
www.kzrider.com/forum/5-chassis/600555-s...-z1-zzr1200?start=36
When that didn't work out I I got a 98 KZP swing arm that is 1 1/2" longer and is beefier than stock. Problem was it's wider at the pivot so I had to shave some off each side, cut the spacer to match, install thick washers over the inside pivot bushings for it to clear then clamp down in the inside of the frame. I didn't want to shave the bushings in case I wanted to go back to stock if this didn't work. It works well with no slop and is solid but it presented another problem. THE TIRE HITS THE FENDER ON LARGE BUMPS! I made a fender extender to move it 2" back so that worked. 
www.kzrider.com/forum/5-chassis/620298-w...-ever-done-it#898521
Changing the front end can be tricky if not down right dangerous if too low. 

I think your original plan will work you just may need to stiffen up the shock preload a bit. In my case the shocks I was using worked with the longer swing arm but I had to adjust the preload to it's stiffest setting. When I switched to the KZP shocks it was too stiff so I lowered the setting and they work great. I still have two more softer settings left. 
As I see it KHI used stiffer springs to compensate for the steeper angle and longer swing arm while keeping the 14" shocks. 
It worked for me.   
Steve

On my Kz1000 Superbike road racer the rear shocks have been laid down. The lower shock mounts on swing arm are in the stock location. The top mounts have been moved about 3 3/4 inches if I remember correctly. That gave me just under 7 inches of wheel travel. I checked the travel without the springs being on the shocks. I had to remove a few pieces from the frame that got in the way of the rear tire at the upper ends of the swing arm travel. Even had to remove the top half on the inner fender too!! The major advantage of having all that wheel travel is the bike basically floats over most of the bumps and rough pavement that I ran across on the street!!!! On the track the rear tire seemed to stay in touch with the pavement a lot more than the bike with the limited shock suspension travel!!!! This was a common modification done to all of the early Kz1000's that were running in the Superbike class some 45 odd years ago!!!!! Funny its the same modification that AC Sanctuary does to their mega-dollar Kz1000 builds today!!!

Here are a few photos of my Kz1000 with the rear shock mount moved to give more rear wheel travel.

 
 
 
 

I put a KZP swing arm on my Z1 that is 1 1/2" longer. That changed the angle of the shocks and lowered the bike. I had to do a fender extension so the tire wouldn't hit it. My shocks were 13" where stock is 14" so the bike was riding real low. One shock came apart at speed and I saw it in my mirror passing me at 70MPH.   Had to put on a cheap set of RFY shocks I had just to ride the bike again. Picked up a stripped down KZP and switched the shocks for a set of repop Z1 shocks and all is good. Turns out the bike is more stable at a ton and the angle is close to the one on the KZP. They moved the top mount forward on the frame but there is a place for a shock mount further forward that's not being used. 
What I'm trying to say is you change one thing it affects other things as well.   Not just plug and play.. 
Steve
rumble.com/v4rugm9-broken-shock.html