Dueling Kz400's

Yes, I agree about the welder. Mine was 30 miles away at the time. I'm doing all the work at my buddy's house. He lives near our work so I stop by there an hour or two before work. It's hard to get a lot done quickly an hour at a time, but it's nice to have the mess at someone else's house.

Plus getting there early (we work second shift) , means I head out to work before traffic gets bad, so even if the bikes are frustrating, the commute is not.

Someone asked earlier this summer about the number of splines on a Kz400 starter. I took some photots and will repost them for anyone searching.

loudhvx wrote: 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.

What is the engine number?
I'm thinking that it is an S model.


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There must be something about KZ400s that invite PO abuse. You should have seen what the DPO on mine thought would be a good airbox.
Hint, it involved PCV and a lawnmower filter.

The bill of sale says 1976 D3.
Engine is K4E 055500
The bike had a starter clutch and front disk brake.


That freeze plug in the starter hole was put there by me temporarily.

Yes, I agree the 400's seem to take a lot of abuse. Maybe because they don't go for a lot of money. But they are a great first bike, what with being full size but very tame and predictable.

So we changed the oil on the D4, replaced the carb holders with new ones, and installed the D3 carbs on the D4. Along the way we played musical carbs so I made some drawing of the two motors/carb holders. I've posted these before but I wanted to put them here to have all in one place.

After doing a quick clean of the D3 carbs, D4 fired up nicely.

However, of course, because the D3 owner did stupid stuff, I discovered one of the enricher jets was drilled out to about 1/16". I guess that was the smallest bit they had? They couldn't just buy one? So the left carb has a drilled enricher jet. All the rest of the jets measured out to be stock. We will have to source one. Probably Jets R Us.

The bike still starts easily, but you have to take the choke off right away.

The D4 had cutoff header pipes for an exhaust system.
Here is what they used for an exhaust hanger:


My buddy scored a very nice stock system at a salvage place in Milwaukee, and he and his son installed it with no issues. New exhaust gaskets. Very nice. A bit quiet, but I bet the neighbors appreciate it.

My buddy's son also did a very nice job on recovering the seat. It was his first attempt... looks very nice. (I thought he just bought a new seat somewhere).
We also did new oring chain, sprockets, and rear tire.

It's coming along very nicely. I personally don't like that yellow Tygon fuel line. We will source some nice gray or black 1/4" lines that are not reinforced to keep with the stock look.

I had this in another thread but wanted to keep it all in context here.

The D4 would start easily and run great for awhile, but the pitted points would eventually cause it to start running rough and hesitating. At first I thought we had some carburetion issues, but filing the points would restore smooth operation. The pit was deep, so filing the points would only smooth out the tips of the bumps. We would only get about 10 or 20 miles before it would start to hesitate. Clearly it was time for new points. I checked the condenser and it would hold a bit of charge so it was not dead, but condensers can fail gradually, so maybe the condenser needed replacement too.

One reason I took on these Kz400 projects was to use them as a test bed for an ignition upgrade I've been working on. So instead of replacing the points, I installed the GM HEI ignition module using points as the trigger. This eliminates arcing at the points and only uses a small current so just cleaning old points should let them work indefinitely. The rubbing block or pivot points will wear out before the contact points do, so a set of points might be good for tens of thousands of miles, maybe a hundred thousand. Dirt and oil might accumulate on the points, so a little contact cleaner might have to be sprayed on them once in awhile. The cam lobe still needs to be lubed as normal and the advancer will need lube as normal. This just eliminates the adjustment and replacement from wear. It also eliminates the condenser.

s3.amazonaws.com/gpzweb/Ignition/GPZhei7pinModForPoints.html

After installing the mod, the bike starts easier and even runs smoother. So far none of the hesitation has returned.
Here's the first start. With the HEI ignition the idle ended up higher. We had turned it up to compensate for the pitted points, but will have to turn it back down. With the ignition sorted we can move on to doing some actual fine tuning of the carbs.

Along the way I documented some differences in the D3 and D4 head castings. I don't think the differences affect any functionality and parts should swap from one to the other with no problem.

very cool ignition mod. What do you think the total cost of that is? seems like a simple cheap way to get a new ignition. nice work and writeup!

DoctoRot wrote: very cool ignition mod. What do you think the total cost of that is? seems like a simple cheap way to get a new ignition. nice work and writeup!

Thanks Doc. I think we spent less than $20 per bike, and probably more like $15 per bike (these bikes only have one set of points and one coil, and inline-four would require twice that). My buddy found the modules at Rockauto really cheap. I think it was a closeout on old stock that they have from time to time.

An inline-four would be more like $40 to $50 total if you have to pay full-freight at a parts store for the modules.

As can be seen in the head photos above, a couple intake screws were snapped off. One was snapped off almost a 1/2" into the hole. That was after the easyout was bale to get part of the bolt out, the bolt snapped inside the hole.

In the same photo you can see the mangled head of one of the other screws I was able to get out in one piece with a chisel.

I had to use a chisel on the D4 head screws as well, but all of those came out in one piece. Now they are replaced with stainless allens.

After a couple hours of very careful drilling I was able to crumple the remains into a little ball and pull it out with a tiny hook I made out of a small spring. I had to do this on two holes. The easyouts were not going to budge them and I didn't want a broken easy out debacle. The threads in the head survived in pretty good condition.