AFR misleading? Plugs tell a better story?

>The PCV needs to feed into the primaries and dump in the vicinity of the idle discharge port and transfer slots. This promotes good mixing with the low-speed circuit.
>The vacuum booster should attach at the secondary side port, and you must prove that the booster is not constantly sucking air.
>The port on the intake is for a Vacuum Tee to supply the A/C system, or the EGR amplifier, etc.
>You need a 10.5PV. Don't pay anybody no mind, just install it. 68s on the primary side is probably too lean, but wait until the 10.5 has been tested.

I ran a Hughes HE2430AL in my 11/1 367 for 4 years. It has a very similar intake lobe to yours, just retimed. It ran on MJs from 70/78&10.5, to 72/80&10.5
>My cam liked some idle bypass air,I think yours will too.My Ica was 63 compared to your 57, and my overlap was 53 compared to your 62,so you will probably need some. My 750DP liked the float set on the low side of the window.
> You must get your transfer slot exposure under the throttle plates,set to; from square to slightly taller than wide. If that means just 14 or 12 degrees idle-timing, then make it so. It's a 4-speed car, you cannot time it like it was a hi-stalled automatic; 14* is already lots. (Well you can, but the engine won't be happy about it; oh sure it will idle nice; but so what, if stumbles on tip-in)
If you do this, you may have to change your power-timing back to in the range of 34 to 36. The all-in can be later than usual because of the manual trans, you won't hardly notice the difference.
>Your cruise timing can be fierce. Numbers in the mid 50s are common.
> If NOT running a CDI ignition,then,get rid of the E-core coil in favor of an Accell Super, the big square-top one; it makes a waaay hotter spark on the same input voltage.
> when correctly done, you should be able to idle her down to 700/750 and don't pay attention to the idle-vacuum. When you idle it down,to reset the transfer-slot exposure, you may have to add idle bypass-air and close up the mixture screws some. Right now, they are compensating for the fuel she's NOT getting from the transfers ........ because of the 18* idle timing. Get this fixed, reset your accelerator pump, and your weirdness will go away.
OK I confess, I got that 223/230 cam of mine to idle at 550 in gear and dragging itself around the parking lot.... with the 10.97 starter gear, which is 4 mph.
> my 223* cam did not like 3.23s off the line with the regular 2.66 low box. I solved it with the 3.09 Commando box, and 3.55s which I have run ever since. Now it's a blip-it and go deal.
Your starter gear is 2.66x3.23=8.59 pretty steep for a 340; compared to mine at 3.09x3.55=10.97, which compares to yours at 2.66x4.10=10.91. A starter of at least 10/1 is a nice easy first gear for even a low-compression 318. I'm not saying you should rush out and get these. But, if your '72-340 is a low-compression engine, the 62* of overlap is not gonna play nearly as nice with what you currently have. Someday, at least get the Commando box, cuz downshifting into 3.09x3.23=9.98 starter at 30 mph, is a wicked fun thing to do.
If you get a chance to swap carbs, a DP is the bomb.


Why do you want to pull the PCV off the primary side? I'm not familiar with that particular carb, but most any Holley from the beginning used the rear port for PCV and a port in an intake runner to power the booster. Just curious as to your line of thought here. Not saying you are wrong, just want to work through your thinking.

OP, between Mattax and AJ they have pretty much nailed it. You dang sure need a 10.5 power valve and probably a 12.5 if you could get one (when I get caught up I'm going to start playing with power valves to see if I can get them to open sooner than 10.5 because I could use it for sure) and I'm waiting for AJ's thoughts on how he wants to plumb the PCV valve.

What Mattax said is equally important. You must tune to the leanest cylinder and when you have that style of intake, especially at low engine speeds you make air and fuel (which do not weigh the same and may not be homogeneous) turn too many tight corners. When this happens, the air can make the turn but the fuel has trouble. And the fuel falls out of the air (for lack of a better term due to my limited education and vocabulary), and becomes what is called wall flow. That is fuel that has separated from the air column and is now liquid running down the port walls and floors.

Most all of that fuel never gets back into the air stream and goes into the chamber and adds to stratification issues.

And you end up with what I believe we see with your plugs. The plugs are both looking a touch lean and also a bit fat.

At this point, you can tune to the leanest cylinder and let it go, or spend some time trying to clean up the distribution issues you have.

I suspect this engine would respond well to using a burr finish on the intake manifold runners. Not to make them bigger, but just to try and get the wall flow issues under a bit better control. Just guess on in this as I've never been able to duplicate the correct burr finish (or what I believe to be the correct burr finish) so I don't do it. But that doesn't mean it doesn't work. Also, not sure how much work like that you can do with an intake of that style without taking forever to do it.

Just my spit balling.