Topic: zx600r carbs

[tourmax]

So, I'm wanting larger carbs since I'm taking my 650 out to 657cc. Most may know that 85-88 ninja 600 carbs are pretty much a "bolt on", but they're getting hard to find and expensive if you do. To get them at a decent price is pretty much a "right place, right time" thing around these parts.

So I started thinking about other years of zx600's. After 88, they went to a "semi-downdraft" design, but it seems the carb spacing didn't change much. I started thinking: why not try them?

So I found a set from a 98, in good looking shape and not that expensive (100 CAD):






I did a couple quick photochops (by matching the scale on several pictures) and it appears the carbs will actually fit in the frame and under the fuel tank.

Problems I'll have to fix:

1. Carb angle. I'll have to change the sidedraft heads to ports that will take the downdraft carbs, mostly because the float bolts are "tilted" and the carbs need to be mounted on that angle to operate properly.

2. Clearance. Obviously, anything that hits will need to be deal with

3. Airbox/filters. The carb bellmouth is anything but co-operative. It's a strange oval shape. But, the set i bought comes with it's oem airbox adapter. So I'll either figure out a way to mount pods or maybe design a new airbox that fits in the available space and 3d print it in ABS.

Lots to do and problems to solve, but should be fun building it!

[tourmax]

hmmm, picked up a set of intake "boots" for the zx6r carbs:



Looking at those, I might be able to just machine off the OEM 650 head intake posts, create a flat sealing surface and bolt them on.....

[Don R]

 I wonder if there are any angled carb rubbers that could be rotated to fit?

[Gurp]

I wonder if there are any angled carb rubbers that could be rotated to fit?

+1
That's kinda what I was wondering

[Tracksnblades1]

I wonder if there are any angled carb rubbers that could be rotated to fit?

They don’t seem to run bad standing straight up in a wheelie…😜

Followed a friend of mine son for miles riding a wheelie on a GXSR 1000 …😜

[tourmax]

So, did some calculations, mostly based on he formula in Gordon Jennings book "twostroke tuners handbook". It's old (1973) but the information and formula's seems to stand the test of time.

I get a 28 mm diameter for a .6 and a 36 mm for a .9 (VE). Most seem to report that a .8-.85 is closer to most "real life" for road going motorcycles.

This site is also selling 34mm mikuni's for the cb500/550: https://mikunioz.com/shop/mikuni-rs-34mm-carb-kit-honda-sohc-cb550f-four/?v=13b249c5dfa9

the zx is a 599 and sucks through the 36mm carbs, but the RPM potential is much higher (12k vs SOHC 9.5K redlines) on those bikes which is where most manufactures spec their sportbike carb sizes for maximum hp output (IE: win the HP marketing wars). the ZX is also a bigger bore (66 mm) but a much shorter stroke (44mm) which makes for a stronger "signal" at the intake port (vs my 62mm bore).

None of this means the CVK 36's will work on my 650, but it does indicate they are probably somewhere in the ball park, if not waaaay deep in the outfield.

I have no doubt there's going to be copious amounts of jet/needle tuning , but that's par for the course when swapping carbs, intakes, displacement, exhaust, etc....

[tourmax]

I wonder if there are any angled carb rubbers that could be rotated to fit?

They don’t seem to run bad standing straight up in a wheelie…😜

Followed a friend of mine son for miles riding a wheelie on a GXSR 1000 …😜

Hmmmm, anecdotal, but an interesting point all the same. Of course, just because it stays running doesn't mean it's carbureting a proper A/F ratio....

[turboguzzi]

leave alone the calculations, these bikes have been around for a long time, so what works and what doesnt is pretty much well documented.
never mind that comparing CV carbs with slide carbs is pretty much apples and oranges....
I understand that its a street bike, right?
So with slide type carbs I wouldnt go bigger than 29mm. likely less if you want nice torque, like 26-27. The Kawasaki VM26 sets can work very well. Those 34mm flat slide mikunis, are totally over the top, just wrong size for your bike, whoever is advertising them for fitting on a 550 is missleading.
CV type carbs have to be about 15% bigger to flow same as a slide carb, so I wouldnt go more than 34mm. If zx600 carbs are hard to find, try searching for ZX-7 carbs, the bike was mfg till the mid 2000's so might be easier to find.

[tourmax]

leave alone the calculations, these bikes have been around for a long time, so what works and what doesnt is pretty much well documented.
never mind that comparing CV carbs with slide carbs is pretty much apples and oranges....
I understand that its a street bike, right?
So with slide type carbs I wouldnt go bigger than 29mm. likely less if you want nice torque, like 26-27. The Kawasaki VM26 sets can work very well. Those 34mm flat slide mikunis, are totally over the top, just wrong size for your bike, whoever is advertising them for fitting on a 550 is missleading.
CV type carbs have to be about 15% bigger to flow same as a slide carb, so I wouldnt go more than 34mm. If zx600 carbs are hard to find, try searching for ZX-7 carbs, the bike was mfg till the mid 2000's so might be easier to find.

Someone on this very board is already running the ninja 34's:

http://forums.sohc4.net/index.php/topic,176212.msg2049511.html#msg2049511



Doesn't seem to any complaints so far.

I suppose your could make the "racebike" argument....whatever. this bike is a play toy more than anything else and I get the most enjoyment form my "toys" when I'm building them.

calculations are important. They're every often not the final word, but they get you in the ball park for real world testing.

yes, i am a retired engineer.

I'll try em out and if they don't work, I'll simply remove them. No muss, no fuss.

Mechanical slide carbs? I haven't touched a set of those for at least 20-30 years......unless you're talking modern flatside race spec carbs that is....

[scottly]

So, did some calculations, mostly based on he formula in Gordon Jennings book "twostroke tuners handbook".

I wasn't aware Honda made a 650 two-stroke??

[Tracksnblades1]

I wonder if there are any angled carb rubbers that could be rotated to fit?

They don’t seem to run bad standing straight up in a wheelie…😜

Followed a friend of mine son for miles riding a wheelie on a GXSR 1000 …😜

Hmmmm, anecdotal, but an interesting point all the same. Of course, just because it stays running doesn't mean it's carbureting a proper A/F ratio....

Rhetorical…Duh…😜

[Tracksnblades1]

So, did some calculations, mostly based on he formula in Gordon Jennings book "twostroke tuners handbook". It's old (1973) but the information and formula's seems to stand the test of time.

I get a 28 mm diameter for a .6 and a 36 mm for a .9 (VE). Most seem to report that a .8-.85 is closer to most "real life" for road going motorcycles.

This site is also selling 34mm mikuni's for the cb500/550: https://mikunioz.com/shop/mikuni-rs-34mm-carb-kit-honda-sohc-cb550f-four/?v=13b249c5dfa9

the zx is a 599 and sucks through the 36mm carbs, but the RPM potential is much higher (12k vs SOHC 9.5K redlines) on those bikes which is where most manufactures spec their sportbike carb sizes for maximum hp output (IE: win the HP marketing wars). the ZX is also a bigger bore (66 mm) but a much shorter stroke (44mm) which makes for a stronger "signal" at the intake port (vs my 62mm bore).

None of this means the CVK 36's will work on my 650, but it does indicate they are probably somewhere in the ball park, if not waaaay deep in the outfield.

I have no doubt there's going to be copious amounts of jet/needle tuning , but that's par for the course when swapping carbs, intakes, displacement, exhaust, etc....

When mentioning Gordon Jennings two stroke tuning , one should remember the source of all the SAE papers…
Gordon Blair and Walter Kaaden come to mind as well as those at McCulloch, Mercury Marine and others..

Calculations are important on two strokes too.
2003 Honda Cr125,  38 Mikuni TMX
2002 Honda Cr250,  38 Mikuni TMX
2001 Honda Cr500,  38 Keihin. PJ

[turboguzzi]

read my post again,
I said 34mm flat slide (as in that ebay ad) = not ok,
34mm CV's (like in that bike pic) yes ok.

[tourmax]

read my post again,
I said 34mm flat slide (as in that ebay ad) = not ok,
34mm CV's (like in that bike pic) yes ok.

The zx6 cv carbs are a flat slide and downdraft design. Not a “true” flat slide, more of a hybrid of round and flat slides:




No need to get your knickers in a knot…which seems to be a fairly common occurrence on this forum.

[turboguzzi]

the carbs in your pix are CV carbs, period. regardless of the shape of the piston.

"flatslides" are purely mechanical operation, so something totally different,

https://www.orientexpress.com/p-5359-mikuni-rs-flat-slide-carburetors-34mm.aspx

https://www.keihin-fcr.com/index.php?route=product/category&path=68

get some education on the subject, once you know what you are talking about, come back to us in the Hipo forum.

[tourmax]

the carbs in your pix are CV carbs, period. regardless of the shape of the piston.

"flatslides" are purely mechanical operation, so something totally different,

https://www.orientexpress.com/p-5359-mikuni-rs-flat-slide-carburetors-34mm.aspx

https://www.keihin-fcr.com/index.php?route=product/category&path=68

get some education on the subject, once you know what you are talking about, come back to us in the Hipo forum.

I have plenty of “education” thank you.

You’re arguing mechanical vs cv slide lift systems.

Flat slides refer to the slide, not the lift mechanism.

So how about we leave it here and you stay away from me, and I’ll stay away from you.

Good day.