3 digit number on tank?

Can anyone help in identifying the number underneath the fuel tank at the rear near the retaining band hook?
This is from my Z1A, build date 06 1974 (owned by me since new) and is about the only code I cannot find a reference to anywhere. I first posted in the new members forum recently with some original 1974 photos and some pre-teardown shots from July 2009.

Any help would be appreciated.

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It's not a code that I have been able to interpret with any certainty.

I have a 73 Z1 - the tank says '8 26'. The tank shape shows it's an early style tank (the V neck). It could be a date code August 26 - but that seems too early as my bike was assembled in Feb 73. I don't know the tank is original for the bike - and that's always the problem trying to validate codes - it's making sure you know with a high degree of certainty that part came out of the factory on that bike. Could yours be April 16? - it's possible as that's within the date code range that would be reasonable for your bike.

[attachment:1]C:\fakepath\100_2201.jpg[/attachment]

[attachment:1]C:\fakepath\100_2201.jpg[/attachment]
Thanks for the response so far - yes the tank is original and the date interpretation of April would fit. Bought in Bunbury, Western Australia, mid December 1974. Without writing a book at this stage, the only damaged parts which have been replaced since new are things like:
- indicators RHS
- points cover
- headlight ear RHS
- handgrips, handlebar

These were the result of a walking pace tipover and a push off the sidestand by a car reversing.Both onto RHS. The tank still has the dent from indicator body in the 1976 tipover.

Apart from about 12 years actually on the road, most of the time has been parked up or in storage, so there has been no need to change much, exhausts and shockies excepted.

Sorry, attachment did not appear to work before.

Hmmm...checked my Z2A tank (1975 model) and it is coded 517. Never noted it before...thanks for pointing it out.

Would seem that the first number is the last digit in the year (4 = 1974) and the next two are the week of production (16 = 16th week or about April) except for Jeff's unless maybe it wasn't the original tank or the 8 was to have been or is a badly stamped 3? Then again it could be a totally meaningless number as it applies to each bikes info and this is just giving us a quarter to find in the corner of a round room.

KZ_Rage,
With other coding using a single digit for the year, this sounds like a valid interpretation as it defines the year again.

Many thanks - although it's an endless puzzle with coding and build dates.

I looked into this years ago and concluded it is no more than a batch code. The picture attached is from a Z1P build date May 1975. The fact there is a gap between 12 and 4 could suggest Dec 74 but this then contradicts previous postings

Are there any 1970's Kawasaki production line workers still out there who can help us?

The puzzle is endless.

These codes are not Kawasaki codes, they would be from the factory that manufactured the tanks. Interestingly, it was from a retired Japanese Kawasaki employee that the code on the front disk rotor was demystified.

We've been able to decypher many of the codes on the bike, but this isn't one that just makes sense (yet).

The tank with the number is off my 75 z1 with an early bild date first or sec day of production and the red one is off my 74 and has no number