Z1-B rebuild - carb renovation

[steve452]

I've got to the stage where I'm rebuilding the carbs on my 1975 Z1-B. I've got the Keyster Z1-B kits but have a query on the needle.

My original is a 5J9 and is as fitted when the bike was new. The Keyster is marked Y45. The profiles look the same and I've measured at three points on the taper with a vernier. Give or take a few percent difference at each point which I put down to measuring inaccuracies on my part they seem to be the same. Can anyone confirm that these are indeed the same profile?

[rick-chuck]

5J is the needle, 9 is the lot number. This information comes courtesy the Kawi Z-series shop manual, just below the jetting chart. If in doubt, go to jetsrus.com and purchase Mikuni needles, the new lot number is 11 (or 5J11). I would do this anyway as you know they are correct. Not to kink your cable, but Mikuni parts ALWAYS work best. Also, this website has a lot of useful information. Cheers, Rick

[zed1015]

If there's nothing wrong with the original needles i'd use them and any other genuine parts from the original carbs.
There's not much that wears despite what people say.
Parts to replace besides obvious gaskets and 'O'rings would be the brass fuel mix screws under the carbs as the points wear or snap off if over tightened, Air screws on the side mainly for the chewed heads..Choke plungers or seals because the seats will be leaking causing rich running, float needles and seats and possibly the needle jet in the base of the venturi if it has worn oval but the latter rarely really gets that bad to cause issues.

[Ultim8pc]

The Keyster parts are good quality, but I would always keep the original needles in preference to repros.

[rick-chuck]

In answer to your original query, Here is a link to show exactly where the needles need to be measured to ensure they are in fact correct. Dial calipers would suffice, but a good micrometer would be best. Good riding, Rick

https://www.jetsrus.com/a_jets_by_carbu ... ikuni.html

[r3sc]

In the link, referring to the table of dimensions for the #5 series needles the dimensions for the 5J9 needle look a little strange.

D2 is 2.52mm dia, D3 is 1.432mm dia and D4 is 1.996mm dia. Could this be a typo and D3 should in fact be 2.432mm dia.

It just seems strange that D3 is much smaller in diameter than the two adjacent dimensions unless the area of engine performance relating to the D3 opening requires much more fuel?

What do you guys think?

[rick-chuck]

Yes. I've done careful measuring of a 5J9 I removed from a bank of '75 carbs and the D3 position comes in at 2.36/.47mm, not 1.432mm. Buggers are a fit to measure, I'll tell ya. Anyway,Jetsrus does list the 5J9, so I assume it is available. ALSO, the 5J11 is 4mm shorter than the 9, so obviously not a later lot no., and NOT interchangeable. My bad. I put new 5J9's in my Z1B and they work well, so perhaps this is all rather "needle-less"...HA!

[rick-chuck]

Here's the maint. manual page with the standard Z1b jets and needle nomenclature.

[Johno23]

Here's the maint. manual page with the standard Z1b jets and needle nomenclature.

That isn’t the spec for a Z1B. The Z1B has 1.5 cutaway, a 17.5 pilot and the needle should be on slot/ groove 2.