Picked up a 76 KZ400 S2 just yesterday. My first motorcycle in about 6 years and my very first Kawasaki.
In a previous life, I lived in the UK and rode a Suzuki Bandit 600 pretty much every day. Events have brought me to New England in the US and I've found myself itching to get back into bikes.
I learned a tonne tinkering around on the bandit but I always wanted to delve deeper into the engine and I've wanted to take on a restoration project for a very long time.

This bike is definitely going to be a project. First things first I need to check the fundamentals and figure out if the engine will run. If that works then both wheels have significant rust damage and need replaced. It definitely needs new forks and possibly a new swingarm. It's gonna be fun!
The previous owner said it had been sitting in a barn for the past twenty years. He couldn't find the key but he did have the original title from 1976/77 which I found pretty amusing.
I enjoy restoring vintage tools and putting them back to work so I will be chuffed if I can get this thing back in working order.

I love finding these communities and delving into all the collective knowledge and experience. Hopefully I'll be able to contribute a little something here and there too!

If you are just looking to tinker, I suggest working to advance the maintenance on your current bikes.  Things like tearing down the brake system and cleaning out the sludge, then rebuilding with fresh seals and brake lines.  Same for the carbs; teardown and replace all the O-rings and gaskets.  Adjust valves.  Grease swingarm bearings and steering head bearings.  Tons of stuff to do on old bikes like our KZ's.  Of course, that 750 K2 would be a nice add.  I'd buy it for the price if the cosmetics are good.  Fixing mechanical stuff it typically the easy part.  It's making the bike look decent that's the challenge.  

wrote:

Hello,

I am new to the Z1 / KZ platform as well as riding as a whole. I’m building up a 1976 Kawasaki KZ900 from box parts that I was given as well as a good condition frame and decent engine.

Are there any inherent problems with the  platform or anything I need to “bulletproof “ before I put the thing together? I’m not going for a cafe racer build or a stock restoration but more something along the lines of a resto mod. Any advice would be helpful.

The KZ "big four" engines are very reliable.  My '78 KZ1000 has about 45k miles on it and it runs great.  Do you have any idea how many miles are on the engine you have?

As mentioned, the brakes are not great.  If you're doing a restomod I would definitely switch to a modern caliper and master cylinder.

The OE steering head bearings use bicycle style 1/4" balls, and over time they dent the race and create a sticky spot on center.  This can make low speed handling pretty sketchy.  Many folks switch to roller bearings, but I just used new factory parts. 

I'm not sure if the rear swingarm pivot on the '76 uses needle bearings or bushings.  But the later KZ1000 switched to four needle bearings.  If you stick with the stock swingarm I'd look into new needle bearings.

For suspension, a new set of quality rear shocks would probably be a good idea.  If you want to get fancy, you can replace the fork damper rods with aftermarket valves.   racetech.com/page/title/GVWHYGV

Or if you're doing a more serious restomod, most people just swap out the entire from end for a modern one.

There are plenty of performance parts available for these engines if you really want to get into it.   kzzone.com/

 

Welcome. As you can tell by my handle, I'm a big fan of the GPz's. The 550s are special. I wish my 750 handled as well as the 550 I had in college.
It looks like you have a plan. I would add foundational; items like steering head and swing arm bearings. And, if you are going to replace the brake lines replace them with SS. Galfer makes a set and offers good customer service. 
Oh and bookmark this page:  Partzilla 1981 GPz550  

Well I do need to work on my 3D printing skills for sure, haven’t really been able to get it right. But I got the rims back from paint and could finish the dry build of the fork and the swingarm/rear wheel.


The Zephyr 1100 fork with a ZR750 rim, Zephyr 1100 310mm brake discs and GSX-R 600 calipers fits like a charm. Rear wheel also lined right up and I need to shave of 8mm from the cush drive to get the chain to run strait. So then it was time to get the engine out of the frame and started with the lover front engine bolt.
Of some strange reason it’s fitted from the wrong side but that was not the problem, the bolt was stuck in the steel sleeves of the rubber mounts. Knock it, turn it noting happened except that the engine mounts started to rotate in the engine block.
Tried to knock it back an fourth and soaking it with penetrating oil, knocked harder and the engine mounts started to come out, but because the bolt was fitted from the wrong side there was no way in hell to get the engine mount to pass the bracket in the frame.


Went and borrowed the heavy artillery, the mother of all induction heater.


Heated, knocked, heated hit it, nothing, heated until the bolt was almost white and the rubber mounts on fire, still nothing.


So sadly I had to revert to sawing of the engine bolt with a lose hacksaw blade. Right it took three hours until I had sawed off the stupid bolt. Funny that the only hard bolt made in Japan had to be in my lower engine mount and the ergonomics left a lot to ask for when I was jacking back and forth with the blade,


There was no way to get in there with an angle grinder without risking hitting the engine case or the frame. Then I had to give up and return the Induction heater and came back the next weekend and continued.


As you can see, me my stupid mutt had not only sawed it of once, but almost twice as I had turned the bolt. The other mounts was no problems at all, they were not stuck at all.After making sure that all bolts were free, I lay the bike down, 


Took of the front fork and the rear wheel off.


Lifted the frame off and the engine was out.


Striped the last little bits and the frame is now ready for welding on the bracket for the brake torque rod and then sandblasting and paint.


//A       

I once had a mercury switch bike alarm that would wake the dead, as soon as the bike was stood up straight it screamed its bloody lungs out...
Works great if your bike is close, then its up to you, baseball bat, lump of pipe, pick handle, you get it, and a little tip, don't waste your time swinging high, swing like you're going to hit them high and drop and take out the side of the knee, works wonders, can't steel a bike, fight or run away with one leg......or so i've been told....

On the ST there isnt a regular Pinion that runs from one side to the other but 2 lugs that support the swing arm like the pic below, once the bolts are gone off then pry nice and easy with a large flat head screwdriver or pry bar.
 

I managed to get a little work done last night and today. I pulled the swingarm and torque bar off, soaked them in a 1:1 solution of Simple Green, and scrubbed them with up. Then I busted out the poor man's powder coat

 

and I think the results look pretty okay

   

Also into the Simple Green went the fork tubes. After a ton of sanding and polishing, this is what I got:

 

That left me with just enough time to mess around with the rear brake. I got it resurfaced at a local shop, and decided to drill it out. I came up with a new version of the pattern I made for the front discs that's a little busier: the front ones each have 45 holes, but the rear one has 60. 

 

That's about it for now. I'm waiting for some Progressive springs and a set of rear shocks (I was inspired by 750 R1's build to get the very same set of Ohlins copies), and then I can start putting stuff back together.

The frame is now painted, I first wirebrushed and sanded the frame, washed it, and then did 2 layers of "rust-milk" as I like to call it (Würth rust converter). Man... this stuff works wonders. I have previously used it on cars, and It's like magic, just look at the difference! And also you need like maybe 1dl of it to coat the frame with two thick layers.






Picture before sanding:


After sanding/wire brushing and applying the rustmilk:


I then waited for it to cure and put one layer of hammerite black semi-gloss paint. (I know spray painting it would look nicer, but since I want the bike ready for summer, that's not an option. Also I honestly believe its way more protected against rust as it is now). The swingarm, triple tree, and the two stands will be painted when removed for service (bearings etc).

Yes     KZQ   thats a 50s servi rear end.
I also would like to ask if you have weighed your trike at the tires?
Mine came out 176 pounds on the front tire and 258 on each rear.   I took these numbers while reinforcing my swingarm. 
I agree with the binding at the swingarm, but again what about every factory 3 wheeler? Am I wrong on thinking the bearings will "lift the bike" before they fail?(total of 1000 lb+)
Basically if the swingarm  binds because of flexing, if it don't flex are we then good to go?  
I am asking questions to poke holes in my theories, not yours.I am wrong a lot ,hahahaha  
you can see the springs I added for the "unsprung" weight. After the springs and mono shock she is SMOOTH.