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TOPIC: Dueling Kz400's

Dueling Kz400's 08 Oct 2019 17:35 #812086

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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.

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Dueling Kz400's 08 Oct 2019 18:01 #812087

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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!
-Vic
_________________________________
'78 kz1000 LTD long term project

'80 kz750G project

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Dueling Kz400's 08 Oct 2019 18:17 #812089

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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.

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Dueling Kz400's 08 Oct 2019 18:23 #812091

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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.

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Dueling Kz400's 08 Oct 2019 18:52 #812093

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I read about the same broken bolt problem in 2005 just before removing the carbs from my 1977 KZ650 to replace the carb holders. I decided to try soaking the carb holder bolts with Kroil before tackling the job. An engineer friend of mine told me about Kroil; I had never used it before, but I figured it couldn't hurt. I soaked the carb holder bolts for 3 days applying Kroil once a day. To my very happy surprise when I removed the bolts they came out with no problems at all. Maybe the bolts would have come out without Kroil, but since then I have used Kroil whenever I find a bolt difficult to budge, and it has always worked well for me. Ed

1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)
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Dueling Kz400's 08 Oct 2019 19:02 #812094

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So after getting all the screws out, we installed brand new carb holders on the D3, but we didn't have any carbs to install. We did some research and found that some companies were selling dual Mikuni VM-30 kits, but they were pretty far out of the budget. We found these Chinese "replica" VM30's for sale at much less than 1/2 the price.

Everybody online that has had any experience with them absolutely recommends against them that they cannot be made to work. "DO NOT BUY!" is the usually comment we see. So naturally we bought two of them. The main theme of this bike is to spend no money unless absolutely necessary, and we like a challenge.

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Dueling Kz400's 08 Oct 2019 19:12 #812095

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Well, I have to say they were about what I expected. We didn't see too many details about what is actually wrong with these carbs so we didn't really know what to look for. While they do appear to be similar to VM30's, there are a few noticeable differences at least cosmetically.

I don't have any experience with actual brand new Mikuni carbs to compare with, but I will say the construction of these replica carbs seem decent. I'm surprised I haven't had to actually "fix" anything on them yet. They hold gas and don't seem to overflow. There is no easy way to check fuel level without some adapter for the bottom jet-access door. But they seem to be set at a workable level. The pipe at the bottom is just an overflow.

The main difference that effects us is the main jets are a different thread than real VM30 main jets.






At first this was a bummer since we couldn't find any replacement mains available. But then it occurred to me, if I was going to make a knockoff carb, I wouldn't go to the trouble of making some proprietary main jet, I'd make it use some commonly available main jet. So sure enough, the main jets from the TK22/ Dynojet / Keihin thread right in and seem to work ok.

And I have a boat load of TK22-compatible main jets... so we lucked out there.

As you can see, though, the internal structure of the main jets are pretty different. We'll see if this ends up being a problem or not.

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Dueling Kz400's 08 Oct 2019 19:20 #812096

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One thing that's real nice... main jet changes take less than 5 minutes with that access plug on the bottom. We just loosen the carb holder clamp, tilt the carb out, and a 17mm wrench takes out the plug.






The pilot jets are directly swappable with easy-to-get real Mikuni pilot jets. They are not exactly the same, but almost the same.

Oh, and yes, we are using the dreaded cheapo, no-name pods that can actually block the intake ports. We are going to try to tackle the challenges of those at the same time.


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Dueling Kz400's 08 Oct 2019 19:30 #812097

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One of the main challenges are what to do about the throttle cables. Some kits include a 1-into-2 cable and others kits don't.

We took a big chance and bought a very low-priced Honda CB200 throttle cable assembly which comes with a splitter. Well it works, but requires a bit of modification to work correctly. The CB200 does not have enough travel in the slide end of the cable. So we had to take out a dremel and remove a bit of the throttle housing. I would recommend cutting the cable and removing the housing to do it precisely. Then re-solder new ends on at the carb end. We dinked around with removeing tiny bits and pieces of housing while trying to protect the cable. It worked, but took a long time and is very tedious.

This allowed us to use the stock Kz400 throttle assembly, but it also allows you to use one of the racing throttles that have 1/4-turn from idle to full. The stock throttle feels a lot nicer, though, so even though it is rat-rod ugly, we are going to use it.









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Dueling Kz400's 08 Oct 2019 19:34 #812098

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Thanks Ed, yeah we have Kroil at work and use it periodically. It does seem good. My buddy only had liquid wrench so we used that and heat and light tapping and let it set for days... all tricks I've used in the past, but these carb holders screws are some of the worst on Kz's. It's the only screws on Kz's that I ever have trouble with. Even the brake caliper bolts and bleeders came loose for me after some struggle. I don't know if it's condensation fwhile running on cold days or what, and it's always the one on the far right, which leads me to believe it's from sitting parhked in the rain.

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Dueling Kz400's 09 Oct 2019 06:43 #812118

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The Chinese VM30 carbs come with unmarked jets.
I was able to measure the mains to be approximately 137 to 140,
and the pilots to be approximately 45 to 47.

Many thanks to Diggerdanh for posting the details of his dual-VM jetting. Here is his build thread... very inspiring, by the way.
www.kzrider.com/forum/11-projects/598619...ramber-to-be?start=0

He saved me some time in getting a starting point for these carbs. Now, since the carbs are not actual Mikuni's, it's not clear that his jetting recommendations apply to these carbs, but it was a starting point at least. He mentioned #25 and #30 pilots so I ordered some #30 pilots to start with. The mains, being near 140, are in the range diggerdanh mentioned so I tried them first.

On the initial fire up, back in July, of the D3 with the Chinese carbs, it ran terrible. It barely started after kicking for what seemed like hours. It was probably only a few minutes in 95 deg heat and very high humidity. It took starting fluid to really make it catch, then it held a very high and unsteady idle. I could tell the jetting was pretty far off but it seemed so erratic I suspected the battery was damaged from deep-cycling, due to the earlier posted , non-functional (to say the least) charging system.

Sure enough, the battery which had 12v a few minutes earlier after coming off the charger, was down to 7 or 8 volts.

So let's just rewire it and put in a smaller, lighter battery, in a less conspicuous location.

First some measurments...

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Dueling Kz400's 09 Oct 2019 06:54 #812119

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The battery is a used item. It is from a computer backup system we use at work. We get rid of failed backup unit from time to time, but some of the batteries are still good, so but my buddy and I scavenged some of the batteries over the years. Once fully re-charged, they make a very handy 12v source for projects. So we thought we'd throw one in the bike. At least it was free.

These batteries can be had for very cheap at industrial battery supply stores... like $10 or less sometimes, but for anyone wanting to use them be aware, they are not designed for automotive use. That is, their armor is very thin as the battery is meant to be fully supported by cushions of some sort and not really meant to be vibrated. So we made sure to make a very flat, supportive base on the battery box and fully enclose a holder around the perimeter. Then we put some thin adhesive, soft rubber pads on the bottom and side supports. The whole thing gently "hugs" the battery.

Our budget demands pulling scrap out of the dumpster and using whatever came on the bike, since that's what we have. So I hacked out and bent up some sheet metal scraps from some discarded machine parts at work. My buddy finished a couple welds and painted it.






We used a Harbor Freight spot welder to assemble the parts, but I'm not convinced it's strong enough for permanent welds. My buddy will tack it with the tig to secure the side bands.







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