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Author: Subject: KZ250 Carb Replacement: Mikuni VM26 *Install PICS*
AbyssDncr
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[*] posted on 9-9-2005 at 12:45
KZ250 Carb Replacement: Mikuni VM26 *Install PICS*



Hey folks,

I know the little bikes aren't that popular here, but I have another carb replacement question aimed at ditching the Keihin CV carbs. As successful as the 440 replacement went, it's definitely worth giving another try.

I just brought home an '80 KZ250 LTD to fix up for my father-in-law to ride around on. It needs a bit of work, but that's what makes it fun, right?! ;)

Anyways, the carb diaphram is torn twice. I had originally intended to replace it with a used Mikuni slide carb from ebay. Then I thought about trying a single Mikuni 34mm cv, but it's physically too big. :(

I was figuring something like a 26-28mm VM, because that's what the 1000s had on them, but then there's the question of carb design....

I see VMs and TMs on ebay occasionally. For example, there's a 24mm TM going shortly...would a 24mm TM roughly equal a 26mm VM? Should I be looking more to a 28mm or 30mm? The single doesn't have any benefit of the exhaust collector improving flow, but the single will cruise at notably higher rpms than the big bikes?

So whatchall think? Size, design, etc.? I need some help with a sounding board, so let me have it.

Thanks!
:cool:



[Edited on 28-9-2005 by AbyssDncr]

[Edited on 2-10-2005 by AbyssDncr]




1983 KZ1100A3: Accell coils and wires, 4-1 exhaust, K&N Pods, rebuilt and jetted carbs, Dunlop K491 II Elites, APE Racing tensioner.

1982 KZ440D3: Wife's bike-lowered, Progressive Suspension 11" shocks, Progressive Suspension Fork Springs, Mikuni 34mm CV carbs, Dyna coil, & Accel wires.
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AbyssDncr
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[*] posted on 13-9-2005 at 20:08
Sometimes I don't know why I persist, because...



...truer words haven't been spoken here in a long time. :(

[quote][i]Originally posted by ibsen22000[/i]
[quote][i]Originally posted by steell[/i]
Nah, don't bother with the baby twin, get the KZ750 twin :D :D

[/quote]

You know, you are right steel. If you wan't to be treated as a serious member of this site, keep away from anything less. ;) [/quote]

But I digress...and I'll waste some more space for sake of suitable CV Keihin carb replacements anyways...

It looks like Jeff at Z1 has found me the proper hookups to replace the OE Keihin 32mm CV carb with a brand spankin' new Mikuni VM26 roundslide.

Also getting a new Mikuni intake manifold. It will have to be slotted at the attach holes as it's built with 60 mm ctc mounting holes and the 250 is 66 mm. Nothing major...

I'm not at all familiar with the throttle cable attachments for these carbs though, so I'm not sure how that's all going to work out, but I'll figure it out as I go.

In the meantime, I'm planning on removing a decade's worth of dirt and grime, polishing the shiny parts, grafting in a wire harness from a 440 because the original one was fried, replacing fork seals, installing tapered roller bearings on the steering stem, and getting her back on the road again.

Cheers,
:-|




1983 KZ1100A3: Accell coils and wires, 4-1 exhaust, K&N Pods, rebuilt and jetted carbs, Dunlop K491 II Elites, APE Racing tensioner.

1982 KZ440D3: Wife's bike-lowered, Progressive Suspension 11" shocks, Progressive Suspension Fork Springs, Mikuni 34mm CV carbs, Dyna coil, & Accel wires.
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steell
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[*] posted on 14-9-2005 at 00:25


Sheesh, I was just joking around with Ibby :P

I doubt if there is even half a dozen people with KZ250's on here, so it might be awhile before anyone answers.

Of course I have a couple of suggestions ( was there any doubt :) ).

Measure the ID of the intake manifold, or the OD of the present carb, it will be a lot easier if you can find a carb that will physically fit. (just read your last post again, looks like you have that covered)

I may have a couple of carbs off a Honda 500 /550 twin, but I think they are CV type, although they may be close in size. I'll go to my brother's house sometime this week and check.

And of course there is always fuel injection (bet you knew that one was coming) :D



[Edited on 14-9-2005 by steell]




5 Kawasaki's:
3 KZ750's and 1 KZ750, and 1 GPz750 :)
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ibsen22000
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[*] posted on 14-9-2005 at 02:59


It is hard to tell, but a 26 or 28 mm VM seems to be a reasonable size. A lot of the two strokes from the 70's used one of these sizes. The 28mm Mikunis from a Yamaha RD400 will work on the KZ400 btw.


Did someone mention turbo;):D




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wiredgeorge
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[*] posted on 14-9-2005 at 04:25


Round slide should go 26-28mm per cylinder I suspect based on what is seen on multicylinder bikes. As far as cables, most of the single carburetors have a cable attached right to the top. It might be possible to use a twin carb VM carburetor if you had the one with the cable pivot mechanism but it would probably be simpler to have a single carb with a pull throttle. I think you will also have to fabricate some sort of bracket to hold the cable so that it can actuate the carb's throttle. Perhaps look at an H2 which used three separate carbs... They use VM28 carbs. You will also need to have a choke cable arrangement.



wiredgeorge

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Two 1976 KZ900A4s
1982 CB900 Custom
1988 Voyager XII
VROC 2420
CMA 74623
Venturers 147/Chaplain
Mico TX
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fixitmann
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[*] posted on 14-9-2005 at 04:26


Hey let me know how your carb swap comes out on the 250.

I had to make a plate to block off the missing spring loaded plate on the choke valve on my 250. If you want to sell the original carb and the part I need is intact let me know.

Did you get your fork seals yet, I may have an extra set.

What carb did the KZ200 have? I think it was some type of "slide" carb. Might look for something off a dirt bike or ATV as well.

If you hear of anyone having a extra head pipe for the exhaust for one of these things let me know I am needing one as the inner liner on ours has cracked and rattles quite an bit.

No there are not a whole lot of 200/250 owners on here :( Too bad because they are great little bikes.:D




"So the old Rocker gets out his bike
to make a ton before he takes his leave." JT


1980 kZ750E1
1980 250LTD
1981 650csr
1980 750ltd (engine is now in the E1)
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ibsen22000
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[*] posted on 14-9-2005 at 04:53


The KZ200 have a Keihin PW26. At least the European version.

I do believe a 28mm VM should work on the 250.
In fact on the race version of the Ducati 250 single, they use a 34mm Mikuni VM.

The choke shouldn't be a problem on a VM carb, since it has got a choke lever on the carb.

And if you need to build your own cable, you can buy kit's from England with both solder nipples and non solder (screw on) nipples.

[Edited on 14-9-2005 by ibsen22000]




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AbyssDncr
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[*] posted on 14-9-2005 at 08:29


My new carb is an aftermarket single VM26 from Sudco which I believe is being marketed for the 2 stroke crowd. However, Jeff as asked Sudco to set it up for my 4 stroke application.

Mikuni isn't doing the VM28 anymore, so it was a choice between the 26 or 30. I went smaller, as it seemed "safer"???

The OE carb still has the choke plate flapper piece, but the little spring which holds it shut is broke. It looked like a PITA to fix, and the diaphram is torn, and it's just a crappy carb...all the more reason to replace it.

"We" bought the bike for $100...so I don't feel too bad about putting some money into it. Provided that I get it running right and on the road in the next few weeks, I'll turn it over to be ridden for the rest of the season. However, when season is over, it's coming back to my house for an overhaul. I don't know why, but overhauling the single just sounds like fun! :D Depending on the cylinder condition, it'll get a hone/rings or .5mm over piston and rings, 3 angle valve job, fresh valve stem seals, etc. Might have $800 in it when it's all said and done, but so what. It'll be a working bike, freshened from stem to stern...literally! With the price of gas these, days you can ride the money back out of it in a single season.

Thanks for the offer on the fork seals, but I think I've already got Jeff rounding up the necessary parts for me. Hopefully, those parts will be in at the end of next week. In the meantime I got to get the wiring all sorted out...and it's a total mess! :(

My exhaust is actually in pretty good shape (I took the muffler part off to polish it because I was bored,) but man is it heavy! I was thinking to myself that the right side head pipe from a 400/440 ought to fit ok, couple that with a little extension from the exhaust shop and a Kerker/Supertrapp can and you could drop 10 lbs easy. Ten lbs is like a whole horse power...that's like a 5% increase in performance right here! LOL! :P

:)




1983 KZ1100A3: Accell coils and wires, 4-1 exhaust, K&N Pods, rebuilt and jetted carbs, Dunlop K491 II Elites, APE Racing tensioner.

1982 KZ440D3: Wife's bike-lowered, Progressive Suspension 11" shocks, Progressive Suspension Fork Springs, Mikuni 34mm CV carbs, Dyna coil, & Accel wires.
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fixitmann
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[*] posted on 14-9-2005 at 10:34


Let me know if you need any specs. I did find an out of print Clymers for the 200/250 at a local independent bike shop and grabbed it up for 10.00. Not my first choice but lacking a Factory Service manual its pretty good.

I was wondering about adapting a head pipe from a twin. You are right about that muffler, it pretty hefty! Wonder what a straight pipe would sound like? No, on second thought probably pretty bad!

With the flap missing I can tell you mine doeen't like to start cold. Since I blocked off the plate it fires right up. It is pretty cold blooded until it warms up, then runs great and milage is around 65-75 mpg!

Good luck and let me know if I can help!




"So the old Rocker gets out his bike
to make a ton before he takes his leave." JT


1980 kZ750E1
1980 250LTD
1981 650csr
1980 750ltd (engine is now in the E1)
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AbyssDncr
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[*] posted on 27-9-2005 at 20:04


Well the VM26 showed up right on time from [url=http://www.z1enterprises.com]Z1 Enterprises[/url] last Friday. Got the necessary adjustments made to the manifold Saturday and fired it up Saturday night. Very cool!

I'm still fiddling with the jetting as Sudco jetted it way too rich. (145 main, 20 pilot) I'm down to a 130 main, and still too rich. Pilot needs at least a 17.5 as well. Nevertheless, it's all details from here. I'll get some pics up shortly...but wanted to update the thread for Howard's sake! ;)

Cheers,
:cool:




1983 KZ1100A3: Accell coils and wires, 4-1 exhaust, K&N Pods, rebuilt and jetted carbs, Dunlop K491 II Elites, APE Racing tensioner.

1982 KZ440D3: Wife's bike-lowered, Progressive Suspension 11" shocks, Progressive Suspension Fork Springs, Mikuni 34mm CV carbs, Dyna coil, & Accel wires.
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AbyssDncr
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Mood: 250 went home..

[*] posted on 2-10-2005 at 06:05


Ok, Update:

Got it all installed. It took a lot of tweaking the little things (like soldering on new ends for the throttle cable...) but it's on the road. I took these shots yesterday; thought I'd show ya'll what she looks like.

I'm still working on the jetting. It arrived from Sudco with 145 mains and 20 pilot. I'm down to 110 mains and 17.5 pilot and she's running good without fouling plugs...but the plug still looks more brown than "light tan". OE jetting on the Keihin 26mm slide carb with the factory airbox was 105, so I'm in the ballpark! :D


Right, Left and Top left:




_____________________________



[Edited on 8-10-2005 by AbyssDncr]

AbyssDncr has attached this image:
img-1128261934.jpg - 0.00 B




1983 KZ1100A3: Accell coils and wires, 4-1 exhaust, K&N Pods, rebuilt and jetted carbs, Dunlop K491 II Elites, APE Racing tensioner.

1982 KZ440D3: Wife's bike-lowered, Progressive Suspension 11" shocks, Progressive Suspension Fork Springs, Mikuni 34mm CV carbs, Dyna coil, & Accel wires.
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