I am helping my retired neighbor with his project which is now in the assembly stage and rounding up some of the missing parts.  The car is a 1/71 build date.  Vin is 19270.   His goal is to keep it all stock.

Are the correct carbs the 3 screw or 4 screw version?  I don't know how early the transition was.

@EuroDat may be helpful. He posted this and maybe has a source of info.

 

4 screw carbs on my car.

I think the 4 screws changed about mid 71, so he should be looking for the for screw version with an E46 manifold.

They were Hitachi HJG-46W ***. I think the three stars referred to a version code.

And the 3 screw version was Hitachi HJL-46W. I found that in a Hitachi parts manual a long time ago. It refered to those numbers for the Datsun 240Z (North America). I don't have the manual and it was long before mobile phones so I wrote it down. It mentioned the flat tops as HMB-46W.

The letters and numbers probably mean something, just like the transmission code, but I'm not sure what.

10 hours ago, S30Driver said:

Are the correct carbs the 3 screw or 4 screw version?  I don't know how early the transition was.

The website for Z carb specialist, Z Therapy (Salem, Oregon), has a nice photo guide of the evolution of the Hitachi-SU carbs from MY-1969 to MY-1972.  It deals with not just the carb and float body styles, but also those of the linkages, heat shields, throttle shafts, air cleaners, etc.  There's also a photo-intensive assembly guide (a lot of the photos in this section have to be clicked on to make them load).

ZTherapy 240Z SU Carburetor Spotter's Guide

Jim, this is from the parts catalog:

So I would say the transition was around the model year change from 71 to 72.

I've been wondering about the changes made to the round tops through the years as well. I mean, I know that the four screws were used from the start through the 71 model year, and then they switched to the 3-screw version for 72, but that's about all I know.

There seems to be differences in the 4-screw versions used over the years (as described on the Z-therapy spotter's guide), but the pics are so small and the details so vague that I'm looking for something clearer.

Do we have any experts on the finer points of the different versions used over the years? There was some stuff mentioned in that thread about the supposedly 31K mile car on BAT (the one that had the 3-screw carbs on it when it should have had 4-scew). They talked about tabs on the linkage ears and rear pointing vacuum ports... Anyone know the details?

Tab width (seems all the 4-screws are narrow)
Float chamber lid shape and mounting screw tabs
Steel or plastic dashpot knobs
Vacuum tab location on balance tube
Hook or no hook on the linkage between the two carbs
Linkage ears (is this the same as the hook?)

Here's the post from the 31K BAT car:    https://www.classiczcars.com/forums/topic/64539-31k-miles-series-i-240z-up-for-auction-on-bat-over-100k-on-first-day/?page=3&tab=comments#comment-608149

 

Nothing like a good detective story.  Here's one possible clue.  Photo is from the BAT listing for a very nice, original-paint January 1971 Z (VIN 19769) that was listed back in 2006.  That car was unrestored and really sanitary (note the fabric-covered rad hose), so I'm 95% confident that it was wearing its original carbs...

Thanks guys for all your input.   Looks like things are leaning toward the 4 screw carbs,  correct me if i'm wrong....

3 hours ago, S30Driver said:

Thanks guys for all your input.   Looks like things are leaning toward the 4 screw carbs,  correct me if i'm wrong....

They should be 4-screw.  I have a 1/71 as well and it too has the 4-screw set on it as others have also confirmed.

Two additional photos of 19769's front carb reveal screws #3 and #4.  Although this doesn't prove that your friend's VIN 19270 came with 4-screws, the two cars were built in the same month and quite possibly in the same week...