1979 KZ400 (And KZ440, now powered by Mikuni)

Alright folks. The magic bit was 2.0 slides. It's not perfect by any stretch but I'm going to wait to do fine-tuning til I have my air filters and fix a few other things on the bike (tires, chain/sprockets, steering head bearings), but then I'm going to ride the hell out of it and see what spots need to be "filled in", but without a doubt it's making more power now than it ever had on those CV carbs.

Instead of typing it all out again, I'm just going to post a link to my Google Document of running notes (and copy the content here for those who don't want to click off-site links)



https://docs.google.com/document/d/1YJNV7SK6QT4QijFAXL--f6dReBW3g5OP-XoRZzr4bwE/edit?usp=sharing



Configuration 1
Carb Setup

Pilot: 35
Main: 170
Needle Jet: P-6
Needle: 6F5 (middle clip)
Slide: 3.0
Air Jet: 2.0
Visual sync only
Running Notes
This configuration runs, but has essentially nothing in the 1/8-3/4 range. Idle is good, with a slight hang once the engine is fully warm.

Carb Setup Notes following are incremental changes from above

Configuration 2
Carb Setup
Needle: 6F5 (4th from top, 5th from top)
Running Notes
Idle seems to have suffered even though the only change was the needle position. Is it possible it’s feeding some fuel even at idle? Midrange is MUCH improved, however. I’d call it “rideable”, though still a bit flat. Definitely goes WAY lean if you crack the throttle too hard. A smooth application of throttle will pull it through the flat spots and top end is reasonable. Feel like 180 mains might not hurt. Constant rate riding in the ~3k range shows no signs of surge...chain has some snatch to it..needs to be replaced.

Configuration 3
Carb Setup
Needle: 6F5 (middle clip)
Needle Jet: Q-6 (What came with the carbs, used/ebay)
Running Notes
This is actually the best configuration so far in terms of power. Idle needs enrichment when cold, but will idle w/o enrichment pretty quickly ~45-50 degrees ambient. Throttle response is poor until it’s run a couple of minutes though.

I’ve been running the bike on this configuration a few days now and I feel like it has a slight surge at constant rate riding (30-50mph), but with the chain being in such terrible shape, I suppose it could be that as well. Sorta hard to tell what is chain snatch and what might be a tiny bit of surging.

After idling for 5 minutes, plugs are pretty black (not wet), but tip and electrode aren’t coated...so rich, but maybe not TOO rich? Leaning out idle air screws even 1/4 turn causes idle to hang ~3k, though so .... ????

I’m going to get the 2.0 slides in to see if that helps the midrange whenever they show up in the mail. I suspect the midrange and top-end is going to go pretty rich based on the fact that other configurations around the internet never use a needle jet in the Q range, let alone a Q-6, so might need to go back to the P-6 needle jets, or maybe just drop the needle? We shall see...

Configuration 4
Carb Setup
Needle: 6F5 (4th and 5th clip)
Needle Jet: P-6 159
“Wire” idle sync, then “$1.55 carb balancer” http://www.powerchutes.com/manometer.asp
Running Notes

(Excerpt from email)

Last night I changed the N/J back to the P-6. Left the needles on 4th clip. This combination idled well, but has a severe stumble at anything over 1/8 (maybe a hair less) throttle. Just faceplants. However, I rode it around the block a few times to warm up the motor and it /does/ low rpm steady state even better than the Q-6 combo. Any hint of surge is gone in the 2-3.5k range. Aside from the horribly stretched chain on there snatching a bit, riding along ~30-35mph in 3rd through 6th gear it was happy as could be.

Took it back to the house and went to full rich clip on the needle. This is a significant improvement. There's still a gigantic hole above 1/8th throttle, but can be coaxed through it, and once the engine is spinning, the throttle can be opened up and it still pulls well once the RPMs are up at full throttle. Guessing this is just the side effect of giant carb throat and little motor. Again I'm noticing the idle gets a bit "wet" sounding though when I pull the needles all the way up. The idle rpm drops by ~200 I'd guess, but the interesting thing is that even though it's barely ticking over fast enough to stay running, a small application of throttle brings instantaneous response. However, holding that small throttle opening, while it responds so nicely coming off idle, the rpms will slowly drop... I think that means it's going WAY rich just off idle? This problem goes away as I drop the needle, but then of course the mid-throttle positions tank. (Oh the joys of balancing the various circuits Honestly, I'm still having fun... It gives my mind something more interesting to work on than the daily grind)

Thankfully my 2.0 slides came in this morning (along with a couple other pilots and 6F4 needles). It looks like according to the Mikuni charts, the 6F4's taper begins significantly earlier in it's length, so that should help with the super lean lower midrange I'm thinking. Also the 2.0 slides should affect that a lot as well.

I don't want to munge my research by changing multiple things at once... what would be your recommendation on what to try first? Would going from the 6F5 to 6F4 needles or changing from the 3.0 to 2.0 slides make more sense based on what I've told you about the current condition of the tune? It seems to me the slide change more directly address the throttle position that is currently most problematic (1/8 to 1/2) with not enough air velocity/vacuum at moderate throttle openings.

Configuration 5
Carb Setup
Slide: 2.0
Running Notes

Well, that just about did it. There is power everywhere now. It /has/ developed a slight surge so I’m going to drop the needles one clip but I’m wondering if maybe I’ll need a shim as it’s so close I wonder if 1 clip will be too much.

I feel like the top end could probably be richer, maybe get the next few sizes of main jets and see if that changes anything in the top end.

Fire up Mr Sully!!!

Hows the progress on the build going in general?

Detto,

The KZ400 has become a side project for the riding season. I want to get the 440 running and in road-worthy shape so I have a spare bike to let friend's ride... Also being able to sometimes tear around on a, relatively speaking, lightweight bike vs my Vulcan 1500 is awesome. I've already enjoyed my little 10 minute tuning rides on it.

The KZ400 that started this thread is still a bare frame. I do have most of the bits I need to build it, but lack the budget right now to powdercoat the frame and buy another set of carbs for the 400's motor. I figure one running bike per winter is an OK rate, so the 440 will serve as the main focus for the time being.

I /am/ slowly progressing on the 400 though.... wheels are disassembled and I'm almost done painting the spokes. Need to drive the old bearings out of the front hub, get those bead-blasted and then rebuild the forks. At that point I can begin to mock up the frame, mount the rear-sets, finish the tail section and seat, and be sure all the other modifications all work.

BLSully said:

Off Topic: Teazer.... Union Grove, IL?

Click to expand...

WI, Just over the border. Turn left for Great Lakes Dragway instead of right to Racine.

Re: Re: 1979 KZ400 (And KZ440, now powered by Mikuni)

teazer said:

WI, Just over the border. Turn left for Great Lakes Dragway instead of right to Racine.

Click to expand...

Oh cool, that's even closer. I am in Mchenry IL. Hafta go for a ride someday.

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Had my brother (Kendrick on here) ride the 440 up and down the street a couple times so I could get video of it being ridden.

New as of today:

JT 15T front sprocket
JT 41T rear sprocket (factory is 45)
DID 530 chain
Side covers (ebayed for $20 shipped with no cracks/missing pins!)
Drilled out broken exhaust stud. Couldn't find a replacement long enough so I'm just using a Grade 10.9 bolt for now (retapped the hole for M6)
Bit of cleaning

http://www.youtube.com/watch?v=XrDDfzrzOmU

http://www.youtube.com/watch?v=KRv72OKbiq4

So the previous owner of this bike had cross-threaded or overtightened the left cylinder's spark plug at one point, leaving "not much" in the way of threads to secure new plugs. I bought a helicoil to rethread the hole, but decided I'd wait til it actually blew out.

Well, it did today So that's the next project I guess...

The joys of discovering PO's hacks

Nice writeup on the carb tuning. Thanks for that. It will help me get through the process I'm going through. I'm just now going through the same thing with my VM30s.

I started off with the 3.0 slides and while I could get it started and idle, I couldn't give it any throttle at all or it would die. However if I could get it past that point, like a couple of times after flooding it a bit and starting it with half throttle, it would really rev at 3-5K plus. It was really rich at idle.

I went back to the stock (for mine) 2.5 slides and it idles great at about 900 RPM and takes some throttle well though there seem to be a couple flat spots. I can drop the idle to about 700 RPM once it warms up but it doesn't like to stay that low, after giving it some throttle it will die. The mixture screws are about 1 turn out and I'm still on the middle clip of the 6F5 needle. I'm starting with 230 mains and 25 pilot. The plugs look really good from testing idle and rolling onto about 1/8 throttle.

I'll start it with maybe half choke but I can't keep them on for long - maybe 20 seconds. But it was about 70 degrees out when I fired it up and began testing so it probably didn't need much choke at all. I rarely used choke at all last summer but I also didn't ride anytime it was less than mid 60s.

But all that has been testing without any load. I haven't ridden it yet or really gotten it warmed up. My next step will be to take it around the block a few times to get it warmed up and feel for the transitions and then retest again.

Best of luck to you but it sounds like you about have it figured out. Hopefully I'll be as lucky.

Diggerdanh, Thanks for the update both here and in your thread. I think you'll find the idle is too lean with the 25 pilot, but again due to the engine/carb differences...maybe not. Mine won't idle long at all on the enrichment circuits....loads up and dies. I've found the best method is to get it running on the enrichment, then as soon as it starts loading up, rev it to 3k a couple times (not too much as oil's not warm yet), and then kill the enrichment....it'll then idle all day.

Once warm, mine will idle right down to 5-700rpm with snappy response with the 35 pilot. After extended idling (5+ minutes) the plugs are black around the edges, but medium brown at the electrodes...In my mind that'd be "just the right amount of rich". Since the VM's don't have accelerator pumps, extra richness at idle seems to help that off-idle response (as well as lower slide cutaways). I do have 25, 30, and 40 pilots sitting around I need to experiment with, but it's running so well as it is I don't want to mess with what works just yet. Nice weather, I should be riding, not wrenching.

That said, I just got the bike plated and insured today, so I took it on it's first "real" ride over to my parent's house (about 5 miles). I figured if I ran into trouble, dad could hook up his trailer and come get me. Fortunately, it ran beautifully all the way there, my brother rode it around their subdivision a bit, and then I brought it back home.

It's worst trait at this point is balking at full throttle application below 5k rpm. I believe this can be attributed to the engine size/carb bore mismatch...I'm guessing it would go away with smaller bodies. I'm going to attempt to mitigate it by raising the needle 1 clip (or possibly going to the 6F4 needles), but I also have a hunch the main jet (170) may be a tad small. Wide open at 7-9k I feel like it's not pulling quite as hard as it could. I've got 180's and 190's on order from Mike @ www.power-barn.com and will see how that affects things.

I've been swapping parts around so much though that needles/main jets only take about 5 minutes to switch out

BLSully said:

After extended idling (5+ minutes) the plugs are black around the edges, but medium brown at the electrodes...In my mind that'd be "just the right amount of rich".

I've been swapping parts around so much though that needles/main jets only take about 5 minutes to switch out

Click to expand...

That's about right where my plugs are now after idling for about the same amount of time now. I'll say that it is much better than my plugs ever looked with the stock carbs - they were always black and sooty and a little wet. I actually thought I must have some wing wear and some blowby that I would have to deal with eventually. But the plugs look great now compared to what they used to.

I'm looking forward to going for a little ride and seeing how the rest of the throttle range works.

Ha - 5 minutes. That's good to know, I guess I'll be there soon too.

Best of luck to you. Sounds like you are definitely on your way. And your experience with these on the 440 will make it even easier when its time to do the 400. I'll tell you this, after having so many data points now from various sources and being able to get a really close baseline I see no reason to stick with the stock carbs if I find myself with another KZ twin. Now someone just needs to gather similar data for VM34s/36s for the KZ 750 twin . Since I know my way around the KZ twins now it makes sense that my next bike should be a big brother of my current one.

diggerdanh said:

I'll tell you this, after having so many data points now from various sources and being able to get a really close baseline I see no reason to stick with the stock carbs if I find myself with another KZ twin. Now someone just needs to gather similar data for VM34s/36s for the KZ 750 twin . Since I know my way around the KZ twins now it makes sense that my next bike should be a big brother of my current one.

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If a good KZ750B comes up for sale, we'll have a proper gentlemanly duel over it My first (street) bike was a '78 KZ750B and I loved it...it's what really got me wrenching on bikes, and someday I /will/ own another one.

But I definitely agree....getting the VM's running on the 440 has been so much fun (and honestly pretty easy) I would do it again in a heartbeat. I'm gonna get VM30's for the 400's motor whenever that bike gets closer to being built.

440 is getting new rubber. Figured in the mean time I should replace the steering head bearings. They were so notchy you could place the bars in most any position and they'd stay there :-\

New All Balls 22-1012 set in the frame this evening... Gotta tap the new bearing onto the bottom of the tree, reinstall, and she'll be good as new. Love those taper bearings...

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a piece of pvc pipe works great to drive the lower bearing on the triple stem. won't damage the bearing if sized right and cheap and easy to get.

Re: Re: 1979 KZ400 (And KZ440, now powered by Mikuni)

Frankenfe said:

a piece of pvc pipe works great to drive the lower bearing on the triple stem. won't damage the bearing if sized right and cheap and easy to get.

Click to expand...

Did exactly that today. 1 1/4" PVC on top of the old bearing race flipped upside down let me pound away on the race, not the roller cage. Took some persuasion but it went on nicely.

Then I decided since the front end is off, I might as well rebuild the forks while I wait for my front tire to get here.

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Well, It took me a few days longer than expected to get the front end back on the bike. But it has new fork seals and oil, rear shocks, steering bearings, speedo cable, tires, and the headlight assembly from the 400. Oh yeah and uni filters for the Mikunis. Darn thing is mechanically not far off from new

I am running the 2.0 slides still with good results. The idle is being finicky... I went down to 30 pilots which improved the idle mixture a lot, but I can't seem to get a good balance. I get them close and then after blipping the throttle a few times it goes off one way or the other. Lots of slack in the cable so I don't think that's it. New points and condenser definitely helped but didn't solve.

Went up to the 190 mains... I think there may be even more room for fuel. Thinking going up as high as a 210 would not hurt. The 190s picked up pretty well though from the 170s. It still leans out a hair at wide open throttle.

Back on the 4th clip on the 6F5 needles... I think I might try those 6F4s and see if that helps at all.

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OK, well chalk up one for being a newbie at carb tuning....what I /thought/ was a good idle was actually a super rich idle + slides being too far open. What this results in is a nice beautiful idle with no enrichment needed when cold, leading me to believe I had found the magic combination to get this bike idling on VM32's.... : : :

In reality, it was going super rich once the motor warmed up and would barely idle, and often would cut out when pulling up to stop signs. It took me some experimentation to figure this out (see below), but finally we're on the right track. The text below is an excerpt from my email to a local guy who's been assisting me via email:



So last night I was trying to lean out the idle air screw on the right cylinder since it was so rich...kept going out a half turn at a time listening for the rpms to change....at 4 turns (not half turns, mind you) out from seated, it began to turn SLIGHTLY faster. At 6 full turns out it wasn't "eight stroking" anymore and picked up about 500 rpm. Obviously the idle air screw spring has no effect that far out, and even if it had, it was obvious my pilot just must be much too large.

I've gone through so many combinations of parts I was thinking I already had 25's in there and was irritated as that meant I was done for the weekend as I have nothing smaller. HOWEVER, I discovered the 25's on my bench while cleaning up and realized I must have 30's in the carbs. So I swapped those out and reset the idle screws to 2 turns out each. Voila! It was now idling about 2200RPM but I got my balancer stick out and turned down the slide stop screws til it was doing a nice 1000RPM. No more dying at stop signs!

I rode it combined about 20 miles this afternoon and it didn't die once, though the RPMs still dip a tad...could maybe lean out the idle screws a bit more, there's no rpm hang so I think there's room to lean it out more.

Also, in between getting frustrated with the idle I tried to figure out the hole in the midrange... I went to the 6F4 needles on the middle clip from the 6F5's on 4th clip and that was just a HUGE mistake. 6F4's don't look like they have that much more taper but it just went pig rich in the midrange and just got all soggy. I initially attempted to go back to the 3.0 slides w/ the 6F4 needles, but that ruined the off-idle response (though it did improve the midrange).

Still, I went back to the 2.0 slides and the 6F5 needles, but this time on the 5th clip, and now with the idle sorted out, it's running just beautifully. There's a bit of a hole around 2500rpm if you try and make it pull hard in too high of a gear, but that's I guess to be expected for slide carbs right? Otherwise, if I'm actually riding it in a proper gear, there are essentially no bad manners anymore. Pulls strongly right on up to redline and doesn't surge at all during steady-state riding.

Final settings:
#25 Pilot
#190 Main Jet
6F5 Needle (5th clip - richest)
P-6 Needle Jet
2.0 Air Jet
2.0 Slide
Float tangs are parallel with gasket base

Hey, new to the site, and new to motorcycles in general. So at the risk of sounding like a complete moron, had a few questions.
I bought an 82 kz440 ltd about a month ago, and so far I love it. It's a bit worse for wear but it runs good. The problem is its missing half of the stock airbox, so I know I want to upgrade the carbs so I can use pods and to get some more power. This thread has been really helpful so far, but I was wondering if aside from the vm32's you put on, is the rest of your bike stock? I was thinking of using your set up as a base line and tweak it from there, if needed. Though it sounds like you've got yours running great.
I'm also planning on converting this bike to a cafe, love the styling and the whole culture associated with it. I'd like to get the engine in good shape and pretty well finished by winter, so I can tear the bike down and start on the cosmetic side. Mostly just some clip ons and fabricating a seat. Any other advice on the 440 would be awesome.