carb choice

[Z1B Alan]

I have a Z1B fitted with carbs from I belive a Z1R, The previous owner fitted them as he claims they are better to set up than standard Z1B carbs?
my question is once i have checked the carbs are jetted to standard Z1R spec, how would you expect this setup to perform. M y main concern is the bike will run rich/weak as there seems to be quite a difference in jet sizes from Z1B to Z1R. The bike is standard in all other respects, Has anyone run this setup? Any coments ideas would be welcome, should i set them up as per Z1R ie float height /fuel level etc.

[Garn 1]

Alan, the Z1R standard carbs would be set for the 1000cc Z1R motor. as such, I would think you would need to adjust the jetting to suit your standard 900cc engine.

Nevertheless, run it for a while to find out how it performs. Such items as the stardard air filters as opposed to pods make a large difference. The Z1R carb on the Z1B should run with just about any setting, you will just have to work out the optimum.

With reference to Clymers manual: (both are 28mm)
Z1B main jet = 112.5, pilot jet = 17.5. float level 24mm
Z1R main jet = 107.5, pilot jet = 15. float level 26mm.

RegardZ

[chrisNI]

The Z1R carbs would be easier to set up okay they had an improved mechanism and are easier to balance, as Garn says they were 28s same as the Z1B carbs. The float height would be specific to the carb so set the float height as per the setting for the Z1R - I think the Z900 is exactly the same, if you have the later Kawasaki manual with the '76 suplement it will tell you all you need to know as they're pretty similar to Z9 carbs apart from size.

As for jetting - if you're running the standard airbox you'd need to go for the Z1B jet size, the Z1R's are smaller (see Garn's sizes) because they got less air due to the more restrictive airboxes on the later bikes and it'll be weak. Same with pilots, it'll probably work better with Z1B sizes. There's a fighting chance those jets are interchangeable if you also have the old carbs but in any case you could probably get them from Allen's.

[Jerry]

I'd leave the Z1r jets in and try it. Z1B jets were different, and some of the reasoning behind that MAY be because Z1Bs run the needle on the 2nd groove, whereas the Z1R (and virtually every other bike i've come across) runs the needle in the middle groove, so by swopping jets, but not needles or positions, you might end up in a right mess!

[chrisNI]

Surely the needles would only affect it coming into the midrange? Still think it will be weak with Z1R mains and pilots with a Z1B airbox.

Jerry's point is reasonable though you've got to start somewhere so you might as well try it as is. Have you never actually had it going and if you have what's it go like?

[Z1B Alan]

Had the bike running. previous owner claimsto have done 700 miles on this setup , as the bike wont be on the road until summer i cant confirm how well it runs i was just hoping for some oppinions in advance.

[Pigford]

Z1B Alan,
The only thing to do is fit 'em and test ride it. Even if you had 2 x identical model bikes, the carb set up could be slightly (or even wildly) different due to variations in wear & tear, valves, cam & ignition timing, etc!
When you start the bike up, warm it up well & listen to it for a few minutes before setting off on a blast! Just run the bike with care for first few miles, do a plug check. Ideally ?50 on a Dyno is worth its weight in gold!
These old girls will run with a margin of error if you don't thrash 'em, we're talking early '70's engineering & tolerances anyhow! Good luck.

[hanskloss]

I have 28mm Z1000J probably carbs on my Z900 A4 with 1015 barrels (cc difference is not too important between 903 and 1015 as I was told), the carbs when I bought them were fitted with 115 (made of plastic) mains and 15 pilots, the bike run about OK till about 4000 rpm and than stuttered especially on quick throttle opening, I had a good look at the jets and the holes in 115 plastic jets were considerably smaller than in 115 metal ones -shrunk?? don't know but replaced with the metal ones plus 17.5 pilots and bike runs sweet in any revs now, as others said it's the matter of try and change really

[Pigford]

Hankloss, there are basically 2 types of jets. The threads are slightly different too! There is a chart relating to sizes & comparing the types. The plastic ones are RD type, probably hex or small round slotted. I shall post details when I find the data!

[Pigford]

Just found the link, very useful this guide,
http://www.ozebook.com/compendium/t500_files/mikuni.pdf
have fun!

[hanskloss]

thanks Pigford, very informative read indeed, I thought the number stamped was directly related to the diameter ie 115 would be 1.15 mm hole drilled etc, how wrong...
in my case both jet types (plastic and metal) used were same type (reverse) round slotted with the numbers stamped on the bigger end and the threads were the same, when discovered tiny difference in the orifice size I just thought the plastic ones were crap and replaced the little bastards hoping I wont have to remove the carbs again (favourite job for all of us ) and luckily it worked