1978 KZ400 B1 - Scramber to be

That exhaust is awesome looking. Did you bend all that pipe yourself (or weld)? Very nice tight work.

loudhvx wrote: Did you bend all that pipe yourself (or weld)?

Thank you! Yes I was inspired by a Classic Octane video on YouTube where he did the same thing for his KZ750 twin scrambler. I had not done anything with this bike for nearly 2 years because I was waffling back and forth on how to get the exhaust done: have a pro do it, buy a diy kit, try to do it myself and fear of screwing it up, etc. In his video he cut up the existing pipes into little wedges and used them along with existing bends from the pipes and welded it back together piece by piece. I got some inspiration from that along with a kick in the pants and did the same thing.

The pipes that came with this were cut short, just under the engine, and there were a bunch of dents and some rust so they were beyond saving. However I was able to use parts of it and along with a straight section of 1.5" mild steel round tube that I ordered online I was able to piece everything together and make it fit. I also bought the 2-1 collector online as well. The muffler is not the one I would choose but it was one I had sitting on the shelf.

I did have issues getting the right pipe that wraps around the frame to fit. I tried many times but I could not get it to be one piece and be able to be removable even when removing the front engine mounts and anything else in the way. I ended up doing 2 pieces with a v-band clamp joining them in front of the engine between the two vertical tubes of the frame. Not ideal but it seems to work well. I figured that it it would work for turbos then it would work for this scenario.

The welds were ugly at first but I got better with practice. I used a flux core welder (because that is what I have) and lots of grinding. I then painted everything with high heat black paint and then wrapped it. It is not a thing of beauty underneath that wrap but it is still sticking together so I will consider it a win for now and a good learning experience and practice.

This is the video that I mentioned. I basically did just this. BTW, he did a whole series on this bike that is worth checking out for us Kawasaki lovers.

I'm amazed you fit that pipe behind the frame tube. I would have bet $50 it could not be done...glad I didn't bet.
It makes my day to see something I never thought of, or thought was not possible.

My last notes, before the exhaust addition, said that I had left off with 30 pilots in the VM28s on this bike. However, when I pulled the pilot jets they were 32.5s. I had trouble getting a good idle and keeping it running enough to even mess with adjusting the mixture screws so I thought that the 32.5s might be too rich. I had no real proof of that and probably should have left them as they were but going down this road did lead me to find something else later. For reference I have 30 pilots and 220 mains in the VM30s on my 76 KZ400. Looking back I think the issues with not running properly are two-fold, one the bike has not run in nearly 2 years, and second I found something else later that may have been the main culprit.

I went down to 27.5. I adjusted the air screw to best idle, about 3/4 to one turn out. The bike was tough to start but idled and revved pretty good while in neutral. But it wanted to die as soon as I tried to put it under any load. I re-watched videos about tuning Mikuni round slides (by Mikuni Oz) and set about figuring things out the right way. The 27.5s were quite too lean so I put in 30s.

But I could not get the bike to start. I thought that there was no way that simply going up a small pilot jet size was the cause. Perhaps I had fouled the plugs. I changed those, no difference. I checked the plugs again and noticed they were oddly pristine like they had not tried to fire at all. Then I pulled a plug and cranked it over and saw I was getting no spark. So why no spark? It was a brand new Dyna green coil. I really hoped that was not bad, it was brand new but I bought it 3 years ago or more. Perhaps it was a component of the electronic ignition that I am running from an 81+ KZ440? I have a spare of everything for that except the ignitor, though I do have one on my 76. I set about swapping in good parts from the 76 when I found the cause - the ground wire to my ignitor had become undone. I plugged it back in and cranked, now I had spark - good spark. I believe that I had been seeing symptoms of this for a while. A loose connection may explain the hard starting and trouble keeping it running with the 32.5. I also had the bike just completely die on me a few times while idling when adjusting the carbs - not sputter and die, just die. Additionally when test riding it around the yard I had some trouble with revving past about 3-4K when under load - part of that may be that the carbs' mid-range still needs adjusted but it could also be because of weak spark.

So once I had that corrected I started testing the upsized pilot jets. The 30s are better, it definitely started right up with no choke (it is 85 degrees out today) and I was able to get a good solid idle and adjust the idle down finally. I couldn't really do that with the 27.5 jets. Also wIth the 27.5s it wanted to surge a bit up and down while idling and it would take a second or two to return to base idle after revving. Not sure now how much of that is due to the jets and how much could be a possible loose ignition connection. But the 30s seem to be quite better all the way around so far.

The tuning directions say to adjust the idle pretty low and turn the air mixture screws in 1/2 turn, waiting 10 seconds between each turn, until the bike starts to stumble. Then turn them out following the same procedure until the bike starts to stumble. The final setting should be midway between the 2 points and should be somewhere between 1 to 3 turns out. I found that with the 30s I get best idle around 1 turn out but it never really stumbles even when turning the air mixture screw all the way in, the idle definitely gets quite a bit lower but no stumble. According to the video that I watched that means that the 30 pilot jets are still a bit to lean. So I just switched back to the 32.5 pilots and buttoned everything back up during my lunch break. Hopefully I'll get a chance to test those tonight. Worst case these are too high and I have to go back to the 30s but I feel good that I am getting it figured out now.

BTW, here is the video I mentioned about tuning Mikuni VM round slides. I really like this method, much simpler, than any of the others I have read online:

Thanks for posting the details!

My buddy has a couple knockoff VM30's we want to try on his son's 75 Kz400D2. We ordered 30 pilots and not sure where we will start with the mains. We have 140's right now, which is what the Dimecity kit comes with I think.

It'll be an experiment. We also have some stock carbs that we are fixing up.

Did not get a chance to do anything last night - the kids wanted to go see a movie. So I had 30 minutes or so to mess with it some more during lunch break today.

The 32.5 pilot jets seem to be the right ones. It started up well (or at least as good as any cold blooded KZ400) and idled well and responded to idle adjustment. When adjusting mixture screw it began to stumble at 1/2 turn out and then at 3-1/2 turns out. So midway between the two is 2 turns out and it seems to idle well at that point. I'll fine tune that setting by feel and reading plugs as time goes on (is it better with an additional 1/4 turn in/out?)

Next is supposed to be the mains before the mid-range but in my last previous test rides I had trouble giving it any throttle - it had no power, stumbled and sometimes died. That may have been in part due to possible loose ignition ground and/or it may have been somewhat addressed by upping the pilot jets. Hopefully I'll get a chance to ride it around the yard and see how it is but I may need to adjust the mid-range enough to get it running good enough to be able to tune the mains..

I wish I didn't have these small updates but unfortunately I have only had a few minutes to an hour here and there to test. I'll have a four-day weekend this weekend so I ought to have plenty of time but I am running out of jets to test with. I might try to find a place locally that has them if the price is not ridiculous.

I am not sure what needle jet and jet needle are in the carbs, I'll have to check if I need to change it but the clip was on the second groove from the top. I moved it down to the middle (making it a little richer) and that was quite a bit better and got the bike to be ride-able. The mid-range is not perfect yet, there is still some stumble just off idle, but I'll adjust more once I get the main jets set.

My VM28s came with 200 main jets in them. Those struggled at WOT. I bumped up to 210s and that seemed to be little better so I think I am going the right way. The only 220s I have are in the VM30s on my 76 KZ400, I had a set of 230s but they are in my Dad's 72 Triumph T120's VM32s. So not counting the 220s in my other bike the next size up I have available from the 210s is 240s - I don't want to make that big of a jump for testing, if it is not dead on then I won't know which way to go. I'm getting ready to order a pair of 220s and 230s but it will take nearly a week to get here. I did not want to rob the 220s from the other bike to test but I may go ahead and do so while waiting for the others to arrive. The only jets I have smaller than the 200s are 180s so I will also order a set of 190s to fill the gap in case I am not going in the right direction and need to go leaner.

The larger mains also seemed to help out the mid-range too - especially from 1/2 - 3/4 throttle. 1/4 throttle still has a stumble.

Keep the updates coming. That is how it is done. I have pages and pages of notes for the 550's for various combinations of exhausts and intakes. And even for one given set of exhaust and intake, you can have multiple jetting solutions. You don't find them until you try them.

They will help me a lot, and I'm sure it will help others who may not post or even be Kzrider members.

Selfishly, these notes will serve as a reminder for me as they have done recently since the 2 year hiatus. It greatly helped to read where I was. But I definitely hope they help others in the future too.

I robbed the 220s from the other bike to test with. I will go ahead and order a pair of 230s but after testing those I feel much more comfortable jumping up from 220s to 240s. It still feels really lean at WOT and a look at the plugs confirms as they are nearly white. Skipping the 230s should not be a problem.

Now my concern is that I do not have big enough jets on hand. I have 240s and 250s. But i’ll Cross that bridge when/if I get there.

Mid range is still getting better as I go up in main jet size too. Everything from 1/4 throttle to 3/4 is pretty good and pulls hard.

It has been starting up and idling on first try. My only small concern at this point is that it idles at about 750 after starting and trying to warm up but about 15-1600 after riding a bit. But I have been wringing it out while testing the main jets and since it is running lean i’m hoping that is exaggerating the issue.

I swapped the 220 mains out and back to the other bike. I put the 240s in. They are better but still on the lean side.

Unfortunately I had a little low speed spill this afternoon due to my own stupidity. The bike seems to be fine. I am a little sore but nothing that will not pass in a day or so. Luckily it was on grass and I have been wearing my helmet on these test runs through the yard.

Tomorrow i’ll inspect everything to make sure all is still good and i’ll Continue carb tuning/testing.

Sacrifices made in the quest for knowledge. Glad you're ok!