ZG1200 Experience 99

[cranky]

ll curious how the pods work out.. I've not read much success
at getting rid of the "heck" box.... Best to Ya!!!!

[Highway Rider]

It's been my understanding that it's not a good idea to use them do to them being a constant velocity carburator.

[cbrfxr67]

Me too cranky. Bumboo did it recently and said that he's done 125 miles on them.

viewtopic.php?f=3&t=12061&p=87166&hilit=pods#p87166

I've never had any luck with pods on a cv application. Was barely tolerable at best. Truly I should just get my other airbox and wait til I'm having a fantastic day plus a patience pill and just stick it on there.

I even considered chopping it down, plastic welding in other words, to where it'd be easier to work with. On my 929rr build I had to make a box to work with that frame and it came out ok,... i dunno

highway rider,...generally I agree but that open, easy to get to space without that cursed airbox is super tempting

[SgtSlag]

Can't remember if I posted this before, but... The ZG1200 has Constant Velocity carbs. The air box is required to balance them all, simultaneously. Watched this happen in the Honda CB750 forum, years ago. They, too, had CV carbs, starting in 1979. You could equip a pre-79 model with Pod Air Filters, but nothing after 1978, due to the CV carbs. There will always be a "flat spot", in the acceleration, so long as you run without the OEM air box. Watched a member of that forum go through jets by the box full, trying, without success, to eliminate the dreaded "flat spot" in the throttle. He spent a lot of time, and money, trying. In the end, he gave up.

The real solution is to install non-CV carbs...

I wish you luck. I would love to see that I am wrong... Cheers!

[cbrfxr67]

Thanks Sgt,....good info.

I usually have about an hour each evening to work on my stuff. So, tonight:
Airbox 1
Me 0
Defeated,...but at least I didn't go bananas, just put everything up & called it a night. Why is it so bleeping difficult?

A buddy asked me, 'how do they do it at the factory?' Surely not like I'm trying to do it I'm guessing.
Want to punch that designer in the face right about now,...

[Nails]

Crickets, indeed.

The air box is required to balance them all, simultaneously.

I don't think it's a balancing issue. Instead, I understand that the velocity part relies on laminar flow, which is disrupted with pods. These also are called "constant depression" designs (for every good reason, I can tell you). The "depression" part comes from shear and Bernoulli (acting to "depress" the slide), which depend on laminar flow. The more turbulent flow (the pods immediately upstream, taking in air from all directions) screws this up.

I also know from small displacement dirt bikes that a big airbox improves low RPM grunt. As an example, Yamaha's TT-350 performs significantly better than their XT350, which is very similar. The TT has a bigger airbox -- the XT cuts into it with the battery. And drilling holes in the airbox (upstream of the filter) does wonders for XT performance.

I believe that the XII's good low-end performance is mostly due to the large airbox volume (both of them). I predict that pods will nuke this.

There will always be a "flat spot", in the acceleration

CV carbs respond to changed velocity, introducing a delay between when your wrist twists and the velocity builds. Notice that the throttle isn't directly connected to the slide, just to the butterfly valve. And the slide is what controls the gas flow for the given quantity of air. (I think this is why CV carbs also are less sensitive to elevation changes than other designs. But not immune to altitude sickness!)

The real solution is to install non-CV carbs...

Yes. Pumpers don't have this delay. (Partial work-arounds include drilling a small hole in the slide and modifying the spring. YMMV)

In a similar vein, the snorkels (I mean the parts of the boots that stick into the second airbox) also suffer from similar turbulence, just not as bad. Air around the snorkel has to do a 180 to get into the snorkel and on to the carburetor. I think they'd perform better with a simple bevel right against the airbox wall, so the air would only have to do a simple 90. I suspect that this is a compromise to muffle the induction noise. But I happen to like induction "noise", and I've been tempted to cut them off and grind my own bevel. I'm just afraid of making it all goofy and rough. (I'm extrapolating from culvert design, something I'm supposed to know about.)
I'm also afraid of taking that damn airbox out, of course.

[SgtSlag]

LOL! You obviously know very much more than I do. Thanks for the information. I understood some of it.

I do understand that the Engineers at Kawasaki spent a great deal of time, and effort, to achieve the best performance possible, with these carbs. As you stated, everything is a compromise. I trust the Engineers knew what they were doing, and that they achieved the best performance possible. The bike performs quite well, as factory configured.

I am not an Engineer. I was an Electronic Technician, however, for over three years. I learned, as a Technician, why engineers do what they do, in designs. I had to reverse engineer their designs without schematics, troubleshoot them, and make repairs. It was fun, challenging, and insightful. I have a great deal of respect for most Engineers. It has taught me to respect most motorcycle designs. Four-wheeled vehicles are another story: their designs are often made to maximize the time it takes to make simple repairs, as they know mechanics charge by the hour...

Six weeks back, we trailered our Voyager out to Colorado. We rode it through the mountains, above 10,000 feet. The only issue we had, was a lack of power. I found myself in 5th gear, with the throttle locked wide open. I was shocked, as we were not moving terribly fast, up a slight incline. I shifted down, and performance improved somewhat. That was the first indication the bike was performing differently, due to the altitude. I was genuinely surprised how well it performed at those altitudes, going up and down many mountainsides. Overall, I am satisfied with the Engineers' compromises with the CV carbs. YMMV.

By the way, we were in the SW corner of Colorado, riding in Oklahoma, New Mexico, and Arizona. We visited the Four Corners Monument, did the tourist thing there. Incredibly beautiful area. Would go back, tomorrow, if we could. If you get the chance, go for it! Cheers!

[Nails]

Six weeks back, we trailered our Voyager out to Colorado.

You should've whistled up. I live near Santa Fe. (Or FantaSe, if you prefer.)

The only issue we had, was a lack of power.

When I rode out east this summer my bike developed a nasty, crusty idle, and I had to fuss with the pilot jets. But since getting back up here in the mountains, I haven't turned them back in yet. I think too-lean jetting is more noticeable than too rich, at least in the idle circuit. I bet you'd have better power with leaner main jets -- but I can't see that being worth the effort involved.

I came across this interesting pup: https://thunderproducts.com/product/dia ... -kawasaki/. I had never heard of it before. Basically, you set the bike up with the leanest jetting you'll ever want (tune it to 12K feet), and then let this device add the extra fuel you'd need at lower elevations. I haven't looked at it too closely, but I think you just turn the dial to change this supplemental fuel quantity (dial-a-jet). I think I'll try it on my new-to-me 1985 KLR 250 -- which also has a Keihin carburetor. But I'm a little skeptical whether it's precise enough to put four of them on my XII, though.

By the way, we were in the SW corner of Colorado, riding in Oklahoma, New Mexico, and Arizona. We visited the Four Corners Monument, did the tourist thing there. Incredibly beautiful area. Would go back, tomorrow, if we could. If you get the chance, go for it! Cheers!

That's home -- I've lived in Farmington and Durango. There are great rides all over the place. But no-ooo, I had to ride all the way to Eastern Tennessee to find a curvy road.

[Nails]

You obviously know very much more than I do.

I'm sorry for always contradicting you, and I don't actually know that much about CV theory. But I've fought with CV carbs my whole life, of both European (Little Brit Cars) and Asian (almost every motorcycle I've ever owned) design. I think they work like this:

Twisting your wrist opens the butterfly valve, which allows more air to rush from the reservoir of relatively calm air in the (large!) airbox, through the carburetor, into the intake vacuum. This air flows past the bottom of the slide, which has a small hole in it. As the air rushes by, it creates a partial vacuum above the slide and diaphragm; and it's easy to see how a cracked diaphragm could screw this up. By Bernoulli, this relative vacuum depends on the velocity of the air rushing past.

The slide (top) part of the carburetor attempts to maintain a "constant velocity": if the velocity increases, the vacuum also increases, raising the slide, which decreases the velocity/vacuum in a feedback loop. It's easy to see the importance of allowing the slide to slide, and I really wish I knew Mr. Leo's secret for polishing the damn things. It's also important for the spring to apply a constant downward force, which is why it's a fine diameter wire with many coils. Some have messed with the spring -- cutting a coil spring increases it's spring rate (whether or not that's intuitive). Also, the vacuum depends, to a limited extent, on the size of the hole in the bottom of the slide. Some have drilled this hole larger to make the slide more reactive; and if the CV lag really bothered me, I would consider doing this. (Google "22-cent mod".)

I don't know how this all works across differing intake vacuums. But I think this Bernoulli effect is somewhat dependent on air density, which may explain why CV carbs are less affected by elevation changes than other carb designs.

So, the slide contraption attempts to maintain a constant air velocity through the throttle opening across the different air volumes needed to work the bike. (The volume of air is regulated by the butterfly valve, the only part directly linked to the throttle.) I think this "constant velocity" goal is to better manage the quantity of fuel sucked into the carburetor. More specifically, the carb attempts to maintain a "constant depression" above the slide, given that the coil spring and simple gravity apply a constant downward force. Frankly, I'm amazed it actually works, and I bet Mr. Goldberg would approve. That it works the same across four different carburetors pretty much blows my mind.

The carburetor has other "windows" in its throat, which go downwards to the fuel. The carburetor sucks gas through these. The primary one has a tapered needle partially blocking the passage. With more air volume, the slide drags this needle upward to where the narrow part of the needle is in the pilot jet. The effective size of this system is the diameter of the pilot jet less the diameter of the needle sitting in it (disregarding turbulence). So larger volumes of air in the throat allow for more fuel in the throat, where it atomizes with that rushing air. This is further modulated by the main jet, stuck into the bottom (which is upstream) of all this. (The other part of the "22-cent" mod is to add a washer to raise the needle relative to it's holder in the slide. This mod gets its name from the cost of that washer.)

There are two other fuel circuits. The pilot screw adds a little fuel (it's properly called a "fuel" screw), so little that it really only has effect at the lowest air volumes (idle) -- this effect is partially due to the location of the window in the carburetor throat. I think this jet is necessary because that slide contraption has a limited effective range that doesn't include idle. Confusingly, other CV designs put this circuit on the airbox side of the carburetor, where it adds air to the mix (an "air" screw). Turning an air screw out leans the mix, the opposite of turning a fuel screw out. Lastly, the enrichment circuit ("choke") is a simple slide valve that, when open, allows more fuel into the mix, as necessary when the engine is cold.

Keihin CV carburetors have two more circuits, which are those two little non-removable jets you can see inside the float bowl. I don't know what they do (presumably further regulate the fuel rate). But I do know that it's necessary to make sure they aren't clogged. When cleaning, run a fine wire through them.

Besides a constant velocity in the carburetor throat, all of this control relies on a stable fuel level, which is why the float height and a functioning float valve are critical. It also relies on that large reservoir of relatively calm air in the airbox. As mentioned, I think this is necessary to limit turbulence, which would fuk up the whole Bernoulli thing that is so vitally important to regulating the fuel volume across different quantities of air. The long airbox boots (that extend into the airbox) might help organize this laminar flow -- maybe it's more than just damping induction noise. And as mentioned, I think pods screw this up by introducing turbulence into the carburetor throat. (But I honestly have no idea why the relatively square slide doesn't make a turbulent mess of it all.)

To my eye, there's no way all of this silliness could possibly work.
But it does.

[ekap1200]

neasy enough and a beautiful upgrade





Got my front springs in yesterday. I think I\'m going to weld up those pea holes for the air ride. Was thinking to tap them and put a screw in but welding would be easier and forget about it.<br/>\n<br/>\nFinished stripping parts bike down. Was glad to haul that frame to the curb for the scrap guy to pick up. Maybe clean up the engine and try to sell it, plus everything else we don\'t need,...<br/>\n<br/>\nSeems to be running well although the throttle cable is not smooth. Tried lubing it and still crappy. I disconnected one side and am thinking of yanking that whole assembly out and replacing it with two cables. Anybody done that?

Don't scrap the boots on the old air shocks, they fit the front fork tube's and will keep the bugs and road hazards from striking the tubes.And it won't cost a dime

[cranky]

... you can get new cheap boots off ebay, get the biggest you can,
take a pair of scissors and cut a slit in'um, and zip tie'um
to'ur fork.... don't think no sneaky bugs will slip in that little
seam down the back... FWIW

(.. got happy fingers, don't know how to delete the dupe....)

[SgtSlag]

I put fork gators on my 1979 Honda, which Honda had ditched by then. I thought they looked good on it. I measured the tube sizes, then I ordered a set to fit. Worked quite well. I secured them in place using two black Zip-Ties, one on top, one on the bottom. This ensured they always covered the fork tubes, preventing bug chitin from lodging in the tube surfaces, cutting the seals, ruining them.

On my XII, I found some foam wrap-around's sold by someone here, I think. They work, but they keep popping off (pressure fit around the head of the lower tube, even after using black Zip-Ties). I may order some proper gators to fit the tubes, like I did my Honda. They make the fork seals last 2-3 times as long. I like the appearance of them on the bike, but I really like the fork seals lasting much, much longer... I replaced the OEM air-assist shocks around nine years ago. Never knew the gators would fit the front tubes -- would have used them if I had known! Cheers!

[cbrfxr67]

ekap1200 that's a great tip. I chucked those things to the curb for the scrap guys to pick up. I did pick up some like the ones cranky posted.

Nails and sarge, great reading there. Good stuff!

I finally got that ahole airbox back on. Prayed to Jesus and got it on Friday night.


Then when I cranked it #1 leaked gas everywhere. Took it off again and float had a piece of dirt from somewhere keeping it from closing. Argony. So that's where I'm at now. Yea fun with carbs.

[cbrfxr67]

Had a good evening last night. Cranked up and sounded great. Now back to reintalling that airbox and some tuning and finally get to sewing this one up.

[cbrfxr67]

Been off and on messing with it. Runs great w the airbox off. Put everything on,... runs like crap. At least I got my airbox install under 15 minutes now.

[triton28]

Have you tried it with the airboxes on but NO air filter? At least that would tell you if the filter was the problem rather than the boxes being the problem.

[cbrfxr67]

I will try that triton!

---------------------------------------------------------
That' didn't help anything.

I'm going to pull them off again, order some jets and stick those pods on there and see what happens.

[cbrfxr67]

interesting article here,... https://aminoapps.com/c/motorcycle-amin ... MJ3Vj1Zn2d

[Nails]

interesting article here,... https://aminoapps.com/c/motorcycle-amin ... MJ3Vj1Zn2d

Yes, interesting.

> With pods, it comes down to not creating a strong enough pressure to open the slide needle in your midrange rpms.

I had trouble following this part of his explanation.

The right diagram just below this quote has tiny arrows that show how the throat velocity creates a relative low pressure ("depression", as in "constant depression") above the slide and diaphragm, as per Bernoulli. But he doesn't really describe what's going on that way, instead implying that there's some extra pressure somehow within the throttle throat, presumably from the air rushing in when you open the butterfly valve (the big red arrows). He suggests this extra pressure somehow pushes the slide upward But that doesn't make sense to me because the air is rushing into the throat because of the intake vacuum. It isn't under any positive pressure.

The carb design uses this incoming air velocity to create a relative vacuum above the slide, so that the slide gets sucked upward rather than pushed upward.

But maybe I'm just not reading it right.

> Basically what I was able to accomplish was to supply a more organized, more constant flow of air to the carbs.

Agreed. I think he's mitigating the effect of turbulence that the pods normally cause.

And I suppose he would call our stock intake snorkels "velocity stacks". Okay.

> but my peformace was 100% back

Seems like a lot of work just to get back to the performance of the stock airbox. The pods do look kinda kool. I wonder where he found/modified those boots -- even stock ones can be pricey.

[cbrfxr67]

Always enjoy reading your commentary Nails!

Still haven't gotten my jets in so I took my other bank of carbs and resurrected them, for the heck of it. I don't know if I'm so much better at putting it on but airbox on in 7 minutes. Got it back together and of course it wouldn't start. I wasn't too disappointed since install went so easy. Will mess with it later today.
I can say that my choke cable was tight and not fully disengaging. Oh well that's how u learn I guess.