I've been working on a couple Kz400's over the summer. My buddy has two sons and they each have a Kz400. One is a 1977 Kz400D4 and the other is a 1976 Kz400D3.
I figured I'd better start posting since I have a lot of photos and details, at least on the D3 which has become quite a handful... thanks to the previous owners, it really should have been a parts bike, but I like resurrecting bikes that were basically on their last gasp of air.
I'm not sure I'll do everything chronologically... I might post recent things before some of the older stuff.
These are both very low-budget bikes. The D4 was purchased for $300 no title. The D3 was purchased for $500 with title. No way that D3 was worth $500... more like $200.
These are photos with parts removed already. Both bikes have tanks and side covers (although the D3 covers are the wrong ones or the frame was altered so they don't attach correctly). There were also a few odds and ends that came from another parts bike that was around very briefly ... that's another story... the owner ended up buying it back to work on... very strange.
First, here is the D4, at least back in July or so. This photo makes it look rougher than it was.
Next is the D3. This photo makes it look way better than it was.
The D4 had a locked up front brake and desperately needed a rear tire and chains and sprockets. We also finished up an oil change that was started earlier. They drained the oil and noticed the drain plug seal was messed up and the oil filter was missing the washer for the spring, so we ordered those parts and buttoned it back up.
After getting the oil change done I decided to hop on and ride it. It actually started up with some coaxing and I managed to go up and down the alley. I could tell it wasn't revving fully so the carbs would be next. We didn't have the tire and sprockets yet.
The D4 uses carbs Keihin Cv32 (or CVB32 ?) with rubber diaphragms and as I suspected they had little tiny rips right near the slide attachment. We scoured the internet for diaphragms, but couldn't come up with any direct replacement.
So we tried some diaphragms from a Honda model. These are meant to be put over the slide after removing the plastic securing ring.
I'm posting these photos to anyone who might want to know what's under the securing rings without breaking them. The slide is machined very thin and then the lip is formed into a "rivet". The diaphragm has a molded-in oring on the lip, which gets sandwiched between the two plastic rings, which lock it in place and provide a smooth, round surface for the diaphragm to form against as it goes up and down. The factory systems is a very good system for longevity, but is not serviceable at all really.
The new diaphragm will just have a really fat, square oring at the lip which will grab the groove of the slide. I'm not a big fan of this plan as it does not make for a smooth curve for the diaphragm to move around. This will lead to a short life, I suspect. But there really is no other option unless you can get lucky and find a source for the original parts.
I was glad those carbs were not useable because it gave me an excuse to do two things I've wanted to do on Kz400's... one was to confirm the older piston carbs can be installed on the first-gen bikes that came with diaphragm carbs. And it also gave me an excuse to put on some new carbs. In our case we ended up with Chinese knockoff VM30 carbs that everyone on the internet says to absolutely do not use. I guess I like a challenge, or I'm just a sucker for punishment. We'll see.
For others who may see this, here are some dimensions for the 1977 Kz400D4 Keihin CV32 diaphragm carb slide.
The diaphragm's OD is 72mm.
The diaphragm's ID is about 24 mm to 25mm.
The diaphragm needs about a 19 or 20 mm dish I think.
The new diaphragm that did not work, I think had a nominal 13mm dish.
In the mean time, switching over to the 1976 Kz400 D3,... I HATE! the previous owner. I would say his tools should be taken away.
We found the linkage on the D3 piston carbs were installed wrong. And for some reason he drilled out one starter jet on one carb to double what it should be but left all of the other jets stock and even the starter jet on the other carb was stock. Why drill one jet, and then leave it?
When we got the bike, I noticed the starter solenoid was missing and that huge battery had been slapped in place of the airbox. That made me curious. You don't need a huge battery if you are only kick-starting.
When I went to kickstart it, I noticed this bike did not feel like other Kz400's. I've spent a lot of time kickstarting 400's and they have always been a pleasure to kick. That is they feel smooth and have very little "kick-back". Meaning when you push your foot down, a firing will not push your foot back up.
This particular bike was painful. Almost every kick would try to throw you up over the seat. And if you weren't ready for it, your ankle was toast. So I looked at the timing. And yes it was far off, too -advanced, of course, so I put it back to where it should be. But I've had Kz400 that were too advanced before, and they didn't kick back like this one.
This bike is the first-bike for my buddy's son and this kickstarting is going to be very discouraging.
I also noticed a bit of noise from the starter area that sounded as if the engine was somehow still spinning after I know it stopped. So off comes the alternator cover. Here's the problem:
I know they did this because they turned it the wrong way, probably with an impact gun. RTFM! It shows it's a left-hand thread. Since they broke it off and decided not to fix it, guess how they attached the flywheel? Epoxy. Yes they used epoxy to hold a flywheel onto the crank. I was hearing the entire flywheel and starter clutch assembly freely spinning and moving about on the end of the crank. It's a miracle it didn't do much damage... a few scratches on the end of the crank.
Along they way to looking at the alternator, I had to remove the starter. Yes it was only held on by one bolt because the other one is sheared off in the motor. I also fond they broke the case end of the starter motor. Here is how they fixed it:
Actually, if you look closely, you can see they broke the case at the other end of the starter too, but there was enough metal left to insert a bolt.
So now the battery and starter solenoid make sense. They were deep-cycling the battery as a total loss electrical system while only using the kickstarter. That would also explain why the huge battery would not hold much of a charge. it would go dead in a matter of minutes with no headlight and ignition-only.
This bike is turning into one of those bikes where everything you check is either broken or done incorrectly.
For example, just in case, I checked the nut for the kickstand... finger tight ready to fall off.
Shifter linkage... bolt loose, threads stripped.
Impressive. I am afraid I would have welded one of the pos nuts to it, and the grabbed his vice grips to turn it out.......
By the way. I think you are absolutely correct about how important it is for a new rider to have a motorcycle that operates easily and reliably. There is enough frustration available in learning to ride, without having to fight a jacked up piece of equipment.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough
Also, there have been questions in the past about whether or not the alternator housing on a Kz400 should have oil in it. Well this one did because the flywheel was as free as a bird. But I believe it should not have oil. Any oil is the result of leakage past either of two seals. There is a seal between the crank and the starter clutch and other between the starter clutch and the crankcase. The crank has an oil hole used to lubricate the starter clutch bearing on the crank.
Notice there is not return hole from the alternator housing back to the crankcase.