Been having a good time working on the tuning of a '66 Hemi. Details don't appear in the '66 Field Service Manual because the Hemi was a mid-year introduction, so you have to look at the '67 FSM.

I have both the '67 and '68 FSMs and for each I calculated the fuel flow area (jet area minus rod area for primaries, jet area for secondaries). and they're shown here in square inches x 1000.

The primaries aren't all that different, but for '67 the front secondaries flow more fuel than the rears, and for '68 that is reversed, as well as the total secondary fuel area being about 25% less.

Any ideas why this was done? Were there significant differences in the engines between '67 and '68?

The 1966/1967 AFB carbs are similar to each other, the 1968 to 1971 carbs are a lot like each other and they have noticeable differences between the 1966/67 carbs, especially on the idle speed circuits and parts to set the idle RPMs
I'm thinking the jetting may be very similar on the early carbs and the same on the 1968 to 1971 carbs
The later carbs work better also

Yes, I got the '67 FSM to see how I'm supposed to tune the hot idle speed with the air screws, since there are no hot-idle screws on the throttle levers. The FSM read: "back them out two turns and adjust the mixture screws for best idle". Somehow I was expecting something more complicated. It's idling over 1000 rpm and spec is 750, so- close the air screw some? Anywho it's running too lean.

Try that, :up I learn my best by doing.

66 and 67 are air bypass carbs and NON emissions. Unless CA only in 67 which did have different CAP carbs.

68 was emissions all 50 states and hence the difference, beside no longer air bypass. 68 transition year and they were changing jetting, rods and the idle jet/bleeds. I assume for distribution reasons and final emission tuning. 69 up stabilized the jets and rods, with the only change being idle jets in 70/71.

Thanks for the info. I have 4139 and 4140 carbs (front/rear), which references say are Hemi spec.

'67 FSM lists 4139 and 4143 for non-CAP, and 4324 and 4325 for CAP. 4140 does not appear.

So whatever the differences between the 4140 and the 4143 are, I'll just have to work around them.

4343 not 4143. The 2 differences are in 67 they moved to the vented top on the 4343. Same as CAP carb in 67 and the future 68 and 69 tops for the rear carb only. They increased the jet size to .080 on the secondary Accel pump side. and .083 on the choke side secondary.

There are some transcribe issues in the service manuals. So I look at that, plus the Carter Service data sheets I have, and document what I find in carbs that look to have been kept original.

I do have a 4343 K6 that has not been restored yet, and 67 D7 set that has been restored if you're looking to get the correct carb.

Thanks, I'll work with what I have.