'75 KZ400

Work has been hectic the last few weeks, (with my ship going off to festivals, leaving me without internet access or time to work on the bike), but I'm back and able to get things going again.

The carbs came apart again, and it appears that the jetting is still stock (I can only imagine how it ran with the pod filters. . .) But, less work for me at least. Also found several complete carb rebuild kits in the box of bits that came with the bike, so the carbs are back together and back on the bike. Even better, the bike started! (and the sparkplug didn't come shooting out of the repaired hole)

Replacing the gasket on the petcock went less well. I put in a new one and gas immediately started leaking out of the seams of the petcock. So I stuffed the original gasket back into it. I'll take "fuel dribbling down the lines" over "fuel running freely out of the petcock and all over the bike" for now.


Short video of my friend giving the bike a test ride. It runs a little rough (the carbs haven't been synched yet, and I need to put new sparkplugs in it, so we'll see how it behaves then), but it at least goes and shifts and stops.

Then, even better, my license plate arrived! (I ordered a custom plate, and the DOL managed to send me a pair of car plates instead of a motorcycle plate. so I had to wait another 3 weeks for the correct one. . .) So I celebrated by taking the bike on a short spin around the neighborhood. (10 blocks or so)



So excited to actually get to ride it! Still needs some work. The bike won't idle below 3,000rpm or so, and I can feel it 'surging' even in 3rd. It also leaks quite a lot of oil from side covers on the engine. (Note the wet spot under me in the photo). I have a full set of new gaskets for the engine, I'm hoping that replacing the gaskets for the engine covers will fix that. (We have to pull the covers off anyway. A previous owner punched a hole in right side one with the rear-brake lever and welded it back up, so I have a nice clean replacement off the parts bike that needs to go on. Plus, we need to figure out why the electric starter won't work). There's also a short somewhere in the electric system, probably because the guy I bought it from re-wired the bike (and admitted he doesn't know much about wiring). If you wiggle the bundle of wires behind the headlight, you can get all the power to cut and then come back. So that'll be an issue to track down.

But hey, at least it feels like things are starting to come together a little bit.

Looks good! For the high idle, check for air leaks around the carb boots. And the starter, you'll most likely have to pull. I'm sure it's corroded pretty good.

Removed the engine covers to replace the gaskets. (And exchange the right-side cover for a nicer one without a repair scar)



Looks like something was rubbing on the repair material on the inside.

Things look pretty clean, though!





Voila, No more big weld mark. And, hopefully, a new gasket will take care of the leaking oil.

The fall rains came with a vengeance, so the bike was moved into the backyard shed. Not a lot of room to work, but at least it's dry.



Opening up the left-side engine cover



The previous owner suggested that the starter chain might be busted, but it looks to be fine.



Which means it's something in the starter motor. Given the bike has some electrical problems already, it might just be a short or a loose wire somewhere, will have to investigate that. . .




With everything back together and the bike filled back up with oil, it now won't start. Trying to kickstart it only got us a rather impressive POP backfire. Given that the only thing we messed with (besides gaskets) was the timing plate and advancer, I think we managed to get things 180 degrees out of sync. (Since we spent several hours fiddling with the timing in accordance to the Clymer's and the Kawasaki shop manual.)

So, obviously, it's been a little while since I posted here. I dropped the bike off at a local shop that specializes in old Japanese bikes to fix the timing (since I was fed up with it). Got a call back that they had taken care of the timing, but upon trying to start the bike, one of the sparkplugs shot out. Obviously, the tap and thread insert did not hold. Which meant: time to replace the entire cylinder head.

Fortunately, the parts bike gave me a good cylinder head (the entire lower end of that engine is a solid block of rust, but the top end was still in decent shape despite sitting out in the weather for years.) Well, a filthy cylinder head, but one with good spark plug threads.




The shop also pointed out that the valve cover had a hole in it. Wonder if that contributed at all to the high idle. Welp, another bit to take off the parts bike. the Hole in question.

Pulled the bad cylinder head off the bike, and broke the seal on the bottom end gasket in the process (whoops)



I then went to the Chief Engineer at my work (a handy person to have) to pull the valves from both head. Hoping that two sets of valves would give me four good ones to work with.

After that, the project sat for awhile. I had no money, no time, no motivation, and no idea what to do next.

But, this year, maybe it's the COVID isolation or maybe I'm just tired of asking for rides places, I decided to look up what to do next. I still don't have any money, but at least now I have time and motivation.

So out came the emery cloth and the engine cleaner to try and clean up the "new" cylinder head and all the valves. Boy, there is a lot of carbon build up. It's going to take a fair amount of elbow grease to get these cleaned up. (the valves after some time spent on them. Still filthy)



The cylinder head is, at least, looking much better.

After some time spent doing some serious scrubbing, the cylinder head and valves cleaned up pretty good.



Next adventure will be lapping the valves.


One query is whether I should worry about the slight discoloration on the gasket surface/how to clean it. I know these early KZ400's are known for top end leaks, and would really like to get a nice mating surface.

1975 KZ400s were the first bikes I worked on during what turned out to be my 43 year career at the Kawasaki factory in Lincoln NE. The first bike that officially came off the end of the line on January 20 1975 was a blue KZ400B with gold and black stripes. The rocker cover being broken on the original engine is not a big deal since you are installing the head from the parts bike, and the head and cover are a set because of the boring of the cam bearings. If you would like to verify the flatness of the cylinder head put a light coat of machinists dye(or spray paint on the surface and then work it around lightly on a sheet of oiled, 600 sandpaper on a piece of glass or other verified flat surface. Did you get your electric starter working? Looking back through the thread it appears to me that the starter or one-way clutch on the crankshaft was the problem.

I've come to appreciate the sound of a parallel twin! Mike

Very cool! I'll admit, I am a bit curious as to what the original color of my bike was. Someone, at some point, repainted it flat blue. And removed the "KZ400" badges from the engine covers, with no sign of the holes where the badges once attached. No idea what happened there -shrug-

Yes, I have the replacement rocker cover and associated bits on my workbench, waiting for the cylinder head to be done. They just need to be cleaned.

I have not looked at the electrical starter yet. My goal is to get the bike running first (even if it means using the kick starter). I suspect it's an electrical issue. When I first looked at the bike, pushing the start button produced a reaction from the starter motor. Now, pushing the button does absolutely nothing. I'll be tracing out the electrical system at some point to track down any possible shorts, and will go from there as I try to better pinpoint what is wrong.

I'm appreciating the simplicity of parallel twins if only because there's fewer bits for me to clean!

You can take those marks off with a quick aquablast. It will come out looking like new, including the combustion chambers. Just make sure to wash it thoroughly afterwards to remove any glass beads.

Unfortunately, I don't really have access to media blasting equipment. I'm doing all my work either in the backyard shed at my grandmother's house, or (in the case of the cylinder head and valves) at my work.

Just reminding myself of why I'm working, by posting some pics of the bike when it was last all in one piece. When I was loading it onto a trailer to take to the shop.



I found a stock luggage rack to bolt on, and transferred over the center stand from the parts bike. My goal with this bike is to use it for day trips and touring, so having some luggage space is important to me. Plus, I think the original luggage racks for the KZ400 look pretty slick. (It also makes the bike a lot easier to manhandle around the shed) My dream would be to find the stock saddlebags from a KZ400A, but those don't seem to come up for sale very often. I'll have to make do with universal bags.