So I kicked her over today...she was 15.8 at startup...after revving a few minutes and then getting off high idle, she was 13.5 @ 7" Vacuum. I know I can improve this. When I was driving her and I opened her up she hit 9.9 @ 15". She is running a little fat.

Going to be fun adjusting because I have two carb's to adjust

Some notes that I have run across:
12.5-13.5 cold startup and as the motor warms up, it should "lean out" to your idle A/F reading. If you start it up cold, leaner than your normal idle A/F, then it will be a bear to keep running during warm up.

Are you running an auto or a manual tranny?

so when cold...I need to bring the idle circuit up to 12.5 - 13.5...and then off high idle it should lean out to 14/15 when the chokes are fully open.....in gear I should be at 14.7 (ideally)

Auto trans

It needs to be richer at cold idle. Then as the engine warms up, it needs to lean out to your N idle A/F reading. Once you come off of high idle, you should be in the 13's or so during warmup. Once you are at full running temp, then you should tune your in D (with brake applied) A/F number. This number is way more important than your N A/F number. Once you have the In D A/F number dialed in, (13.5-14.5 or so) then your N A/F will be what ever it is. You will need to test with your in D A/F number. Depending on your setup, your car may idle with a higher vacuum reading around 13.5 or it may idle in D with a higher vacuum reading at 14.5. The main goal is in D (with brake applied at full running temp), is the highest vacuum reading.
What I have found is that an auto car needs to be richer than a manual car due to the extra load at in D idle. It will also be different from car to car depending on timing at idle, air temp, sea level, etc.. No one will be able to give you THE correct A/F number for your setup. Let us know what works for you.

Note: Mine idles best in D at about 13.4-13.6. As it approaches 14.0, the idle gets choppy and the vacuum drops.

I don't run a choke. My car idles in the 16+:1 range on cold startup but I keep it down with acc. pump shots for a minute until I can get going on the road. Hot is low/mid 13s. I can lean out the idle more but it makes it more prone to stall on braking after a blast.

I tune for good street manners and clean plugs more than economy or stoich

""I can lean out the idle more but it makes it more prone to stall on braking.""

Radar,
I found this same problem when I tried leaning out my in D idle A/F into the mid/high 14's. I would slow down to a stop and my idle would start to fluctuate and I would have to kick the accel pedal to keep it going. After a few stops I richened it back up into the high 13's and it quit doing this.

Good point!

I already run an electric fuel pump, maybe jet extensions would help? Haha breaking you quoted me before my edit to braking went thru.

I fixed it. No one but us will know.

I have jet extensions in the rear but I still had the issue when running lean.

Thanks

2013: I just wanted to give a few updates for those who might be interested.

The first item is for WOT tuning. I have always thought that once you have the primary side tuned and then you have the secondary pump cam tuned, then you just change the secondary jets to tune your WOT a/f reading. On some carbs this is correct, but a cool thing that another member pointed out to me last year (and I did not believe him until I tried it) was if you have adjustable HSAB's, you can use them to tweak in your WOT A/F ratio without opening up the carb and changing the jets. For those who already know this, then this will be worthless info. For those like me who did not know this, I can tell you what I learned.
I have three sets of HSAB's (.033, .036, & .039). I started with the middle set (.036) and then I jetted the secondaries until I obtained a 12.5 WOT A/F reading (My WOT target reading year around). This allows me to just swap in the secondary HSAB's to lean out the carb apx .2-.4 or richen the carb by the same amount as the outside weather changes instead of opening up the carb and rejetting when the temps change. So in the Summer heat, I can swap in the .039's and in the Spring/Fall, I can swap in the .033's and depending on the outside temp, these two changes keep me right around the 12.5 A/F mark. I am still stagger jetting my secondaries to keep both A/F gauges close side to side. The passenger side is 2 jets leaner than the drivers side.


Another issues that I had last year was at cruising speeds (40-70mph) and then lightly giving more throttle (transition circuit, not mains), the A/F would lean out into the high 14's -15 until I pressed down enough to start the mains or until the seconds kicked in (DP carb). Since I was in the 15-17" vacuum reading range when this was happening, I was trying to cover this lean spot with the front pump cam/squirters. I made several cam/squirter changes with no real A/F changes. Keep in mind that my cruising A/F from 40-70mph was in the 13.8-14.0 range (E10 stoich = 14.1), so I did not want to change the cruising A/F, I just wanted to add more fuel during light accel at cruise. With this setup, I did not think that the main jetting was affecting this issue since I was seeing the 13.8-14.0 A/F readings from 60-70mph (I am on the mains at this highway speed.). I was using small IAB's (.054 to .060) to allow this to happen with 63 main jets. This combo cruised nice but I am now finding that this was my issue. Even though the cruising A/F looked good, it appears that when the carb was transitioning into the mains, that this was causing the lean readings at cruise to light accel.
This spring I am playing with the main jetting and the IAB's to once again obtain a 13.8-14.0 cruising A/F reading but with using 65 main jets. The first time out after swapping in the 65 main jets (no IAB changes), my cruising to light accel richened up to upper 12's to upper 13's which feels allot better. But my cruising A/F (40-70mph) dropped and my 60-70mph A/F readings are now 13.0-13.2 (mains) and my 40-60mph A/F readings (idle/transition) are now 13.6-13.2 which is richer than what I want to be. I will be able to lean out the cruising numbers with larger IAB's to get me back into the upper 13's but I need to see if that leans out the cruise to light accel numbers too much. Worse case if the 60-70mph A/F stays too rich but my 40-60mph leans out like it should, then I will swap out the primary HSAB's from .036 to .039 which should lean it out about .5 or so on the meters.

I test drove the .064 IAB's and the 40-60mph leaned out to 14.4-14.0 and the car just sounded off at that A/F reading in 60 degree weather. The mains only leaned out to 13.2 so the IAB's only helped out up to about 55mph or so.
The next move is to lean out the 60-70 (mains) into the mid 13's and leave them alone. I will also go back to the .060 IAB's to richen up the transition circuit back into the mid-high 13's and test drive it for a while.

Y07_A66, this is a very interesting and comprehensive thread, I love it!
Now.... did anyone ever do all this on a Carter/Edelbrock carb?
I have a 493 stroker in my Challenger, stock intake, AVS Thunder 800 carb, quite big headers, 3:23 gears and automatic trans.
Idle vacuum is at 14" Hg in N. Cruising is at 20" starting at 35mph until I stopped logging at 70 mph.
I know that adjustment possibilities are not as vast as on the Holleys and derivates. After reading all this I am a bit concerned about the adjustments of the transfer circuit (or the lack of) which is needed up to 50mph on my car. My idle is at about Lambda 1.0 (AFR 14.7) and doesn't seem to change regardless of tuning the Idle mixture screws. Cruise up to 50mph is at about the same AFR, slightly richer, which is ok for me.
Any hints or links for a thread on a AVS carb, especially tuning the transfer and idle circuits?
Sorry for highjacking, though...
Thanks
Jens

My recollection from the last time I looked at edlebrock instructions (helping a friend) there are two idle restrictions. Otherwise the idle transfer circuit is similar.

My guess is that the cause is the same as it would be on a Holley. If the idle mix screws are not getting any response, then most of the fuel is feeding through the transfer slot. See if you can close down the throttle plates a little. If the engine rpms drop to much to support idle in gear, then try increasing initial timing a 2 degrees.

I checked the position of the throttle blades yesterday. The transfer slots are exposed in that they look just a tad taller than square. I think that should be ok, the blades are not too far open.
Maybe I should try more initial timing (is 15° now).
The rpm difference between N and D is not high. I'd say 100rpms or less.

Its good that you looked at the transfer slot exposure. Next time take it one step further and write down how many turns to close them off completely. This way you'll know the relationship between turning the screw in and the slot exposure.

That said, at this point the question is why the mixture adjustment screws aren't having any effect. The fuel to idle is getting drawn from somewhere and the transfer slot is the only logical location.
On a Holley, the transfer slot itself is the restriction (and also picks up air from above the blade). However, my recollection is that on at least some Eddys, there is an additional restriction just for the transfer slot. Even so, assuming that internal restriction is not dominating, slightly reducing the transfer slot opening below the throttle should send more fuel past the idle mixture screws.

The shape of the transfer slot opening is based on a several assumptions which may not hold true in your engine or even your carb. As far as the latter goes, even amongst Holley 4150/60s, some slots were made wider, some are cut taller and so forth. As a result the 'square' can not be relied on for every version or list number. Its just a starting point that works for most. The engine's characteristics at idle and off idle will determine where it should be. With the strong vacuum your engine is producing at idle, it probably needs less than many hot rods.

Edit: After re-reading your first, is it just that the AFR doesn't change with the mix screws, or is it that the mixture screws have almost no effect on anything? In other words you can turn them to nearly closed and the engine rpms don't drop. If the screws don't effect rpm and manifold vacuum, then what I wrote above is relevant. If they do cause the rpm response, then adjustment to AFR is probably going to come from an internal restriction(s).

The mixtue screws don't affect idle quality much and they don't affect AFR. AFR will always stay at about 14.7 (I measured Lambda 0.99-1.00).

The idle speed screw needs exactly one turn until the blades touch the venturi bores, or until the screw doesn't touch the throttle lever anymore.

Today I openend the MP distributor. I took out the heavy spring for a lighter one to get the mech. advance in earlier. Also I shortened the advance slots to raise initial timing by about 3 degrees and retain total mech at 34. Unfortunately time was running out and I couldn't start the engine for check. That'll be next.

yo7_a66
Do you have any updated results from your testing this summer since your last post? I have been following along and have used alot of your suggestions on my quick fuel 750ss carb. My motor is about the same set up as yours only on a 67 barracuda. I love this post it has been great information.Keep it coming
Pat Faley
East Peoria IL
67 Barracuda notch back
69 barracuda project covertible

This Summer I was tuning with the different float levels. I started the Summer with both floats at the bottom of the sight glasses. I was able to achieve a real constant A/F range from In Gear Idle to about 65mph and I was happy with it. But I found a problem when I started testing my WOT A/F. 50mph to WOT was not bad, but idle to WOT sent my A/F gauges into the upper 14's and I had to let off.
I kept getting the carb leaning out on the top end so I started changing secondary jets with no real change. Then I started changing HSAB's with no real change. Then I decided to move the floats from the bottom to the mid line and my problem stopped. Now I could control the A/F better on the top end. So that problem was solved but my cruising A/F numbers went way rich on me so I had to start over again with my Idle In Drive to 65mph cruising A/F's. I knew that the float levels changed the curve of the entire carb range but this showed me exactly what that meant.
When I had the floats at the bottom, I used richer IAB's (.060's) to get the cruising A/F's where I was happy. Then when I raised the floats, I knew that I had to change the IAB's so I leaned them out a little at a time. I used (Front/Rear) .060/.060, .065/.060, .065/.065, .067/.065, .067/.067, .071/.067, then I ended up with the .071's front and back. After each change I wrote down my In D A/F plus 40/45/50/55/60/65mph readings. I also tested with different Main HSAB's to try to bring the numbers down doo. I tried to do these tests with the outside weather within reason to keep the tests accurate.

This morning I test drove with the latest changes with the best results. I now have the same results that I had back earlier in the year when the floats were at the bottom of the sight glasses, but with no leaning out issues at WOT.
I am once again happy with these cruising numbers (E10/9.7:1 comp/with Vacuum Advance):
Idle In D: 13.2-13.6
40mph: 14.0
45mph: 14.2
50mph: 14.2
55mph: 14.2
60mph: 13.8
65mph: 13.4
As you can see, my total A/F range goes from 13.4(ish) at idle in D to 13.4 at 65mph. You can see the gradual changes through out the range as the rpms go up. Going with these numbers, it appears that my mains are starting to kick in around the 60mph range. These numbers were obtained with the following carb setup:
64/78 jets, .071" IAB's, .039" HSAB's, .033" IFR's.
My 50mph to WOT A/F numbers are in the low to mid 12's (12.2-12.6 between both A/F gauges) at the shift point.

This shows the affect of the float levels. So when you move your floats around, it will affect the idle and all the way up the carb setup. (I know that allot of you already knew that, but this is for those of us still trying to get the hang of this.)

Once again, I started this thread to learn more about carb tuning and to try and learn why DP carbs were known to be difficult to tune on the street. What I have learned is that I can see why the older DP's got the reputation of being tuff to drive on the street, but these new DP's with adjustable circuits can be very efficient on the street too. Most of the above tests were done with the carb on the Idle/Transition circuit as it appears that my mains do not affect the curve until farther up the rpm range.

Thank you for the update.

Cruise to Light/Medium Throttle A/F (No Secondaries):
When I first started I was cruising 40-55mph or and I was showing a lean reading when I went to light/medium throttle during a steady cruise. I found the A/F leaning out into the mid 14's. I started by testing Primary squirter size changes with no affect. Then I started testing larger Primary pump cam changes with little to no affect. Then I started on Primary HSAB changes and this showed a change. I then tested Primary jetting changes and this too showed some affect. I then tested Power Valve Channel Restrictor changes and this too helped. So I found that the PVCR's/Main Jets/Primary HSAB's all had an affect on the cruising to light throttle affect. (Note: I use a 10.5 High Flow (4 door) pv. which is the highest rated/highest flow pv)
After I had my cruising A/F under control (see previous response), I knew that I could not modify the Main Jets or the Primary HSAB's without affecting the cruising A/F. But since the Primary circtuit seemed to affect this issue, this left the PVCR's since they do not affect my cruising A/F readings.
My carb came with .059" PVCR's. I bought the remaining larger sizes from QF which were .065/.067/.069/ & .071's to test. I tested with each size and I found that the larger I used, the better the car felt and the richer my light accel felt. (Note: My current primary jets are four sizes smaller than the original jets in the carb from QF). Once I had the .071's in there I still wanted more fuel during this situation. I then drilled out my .059's to .078. (Note: I am not sure that a PVCR can go much larger than the .078" without worrying about the material cross section at the threads. I was very carefull when screwing in these bleeds not to break the threads since the hole is now larger.) The .078's really helped out the cruise to light/medium A/F rating.
I also tested some more after having the .078's in there. I tested with smaller and larger HSAB's to see what would happen. What I found was that the larger the HSAB, the leaner the light/medium throttle would get. Then the richer the HSAB, the richer the light/medium throttle would get. So I ended up with the .039 HSAB's since this was what gave me the cruising A/F that I wanted.
I am still finding out that I can get allot of things close, but other areas of the fuel curve will be affected. I am good with what I've got.

My next testing will be with the secondary linkage adjustment. My QF carb comes with different secondary linkages for 1:1, 40% and 60% delays. I have messed with this a little in the past but now since I have my cruising A/F reset, I am going to revisit this setup. What I have noticed in the past, since I have a short stroke motor, I have noticed that in the cooler weather the 40% worked great but not in the warmer temps. I found that the 60% worked better in the warmer temps but left some throttle response on the table in the cooler temps. This is basically like tuning a vacuum secondary carb. The springs can speed up or slow down the activation of the secondaries. The trick to the DP carb is to keep the secondary cam/squirter to a minimum and not flooding the engine when cruising at slower speeds and then going to WOT. I am currently using the smallest rear pump cam (black) with an 035 squirter with excellent throttle response both at slower speeds and at 50+mph to WOT. (Note: my 3800 converter helps this issue out too.)

Done for now.

THREAD UPDATE:

I am updating this thread due to the request on the General Forum:

I have been tuning out the medium/heavy throttle A/F reading (once the PV is open but no secondary down shift). Since I have drilled out my PVCR's to the point of no material (.078") left before breaking in half, I have been messing with the primary HSAB's and the primary jetting. My carb came stock with 68's and I have been doing testing from the 68's down to 58's. I have also been doing testing on the stock .033 primary HSAB's up to .042" HSAB's. Since my problem was while cruising and I press down on the accel pedal until the PV opens (8.5), then my A/F readings were in the upper 14's. With the combination of the stock .033 HSAB's/.078 PVCR's, and 67 primary jets, I am now getting mid 13's under this same condition. The car is very responsive since sticking with this setup. It likes it a lot!!!

Another change for this year was swapping from 89 octane to 91/92. I have had to richen up my in D A/F (last year and this Spring it was at 13.8-14.0) and my cruising A/F and my WOT A/F. I am thinking that my local gas station must have changed gas again. It is UP TO E10 just like last year but I had to richen up the overall A/F by about .5 point. The car runs great at this level too!! Richening up the in D idle from 14.0ish down to 13.5ish helped a bunch on the cold start up and the hot startup. Both of these were a bear to keep the engine running but now since I am at 13.5ish, it is much easier to manage at both cold and hot start ups.
I have driven the car with the below setup now for a week or so in cooler outside temps and I am at the point where I can't change anything without compromising the A/F in other driving situations. I Now have a "middle of the road" setup. I always read where you can only tune a carb so much and that you have to pick your battles on what you want for readings. I have found my best setup since tuning with the two A/F sensors and on E10/91-92 octane.

This is my current setup:
In D idle timing: 32 (FBO "manifold vacuum" distrubitor, 18 initial, + 14 at idle = 32, then 34 total + vacuum advance) This makes starting the car and shutting the car off much cleaner. It has 32 degrees timing once the engine is started. Once the engine is cranking or shutting down, the timing drops to 18. I love this setup!
I have a idle stop solenoid wired into the NSS that allows me to separately adjust my D/2/1 idle rpms versus my P/N rpms. I can run 900rpms in P/N and then when in D I can run 1000rpms which allows the alternator to spin fast enough to keep the electrical gauge happy. I love this setup too.

You will see from the next numbers that I am currently charting my A/F numbers from in D to cruising at 65 mph and I get the A/F range from 13.4 to 14.0 to 13.4. The readings are nice and steady all the way up and down.
D: 13.4/13.6
40 mph: 13.8
45 mph: 13.8
50 mph: 14.0
55 mph: 13.8 (mains starting in:2700rpms)
60 mph: 13.6
65 mph: 13.4
NOTE: My engine starts to surge around 14.4 A/F.

I only test my WOT A/F by cruising at 50mph and going straight to WOT. This give me a good test procedure every time. Last year I was aiming for 12.6-12.8 but it was not as strong as I think it should have felt. This year I richened up this number to 12.2-12.4 and it feels great!

My current Quick Fuel carb is a SS-750-AN and this is my setup:
67/75 jets
IFR's at .033" (Metering Screws outward 1/2 turn)
.033/.036 HSAB's (I tune the secondary HSAB's to get me the WOT A/F desired after outside temps change year around.)
.050/.060 IAB's
Red/.037 both front and rear
Secondary linkage set on 40% delay
Bowls are set to 1/2 in the glass per QF
Idle fuel psi at 6-3/4"

This setup is a blast to drive. At a stop in D, I can mash the throttle and have instant tire spin. I might have to get some stickier tires next year. Any where in the cruising range I can mash the throttle and have instant acceleration.

I love this carb and my wideband sensors!!

This is an awesome thread that should not be lost. Add it to the archives ????