Another update:
82 degrees HIGH humidity. I swapped back to the 9.5 High Flow power valve and the bottom end power came back. This carb definately needs the HF unit per QF's recommendation. The 50/55mph cruise to WOT did not change but the response was excellent at all driving rpms.
I also swapped the .031" secondary squirter for my smallest .018" squirter and found no change on the 50/55mph cruise to WOT rich spike. I think that I will live with this since the spike only happens for a second before the A/F starts to rise.
This was the first attemp from an idle at a stop to WOT all the way up to the 2-3 shift and I was surprised to see both 1-2 and 2-3 WOT A/F readings showed 13.0 in the same run from a stop all the way up thru the shift points.
Do you think that the 13.0 is a safe WOT reading at the shift point?
Each 50/55mph to WOT showed apx. 12.0 spike and then climbed to the 13.0 mark. I am wondering if delaying the secondary pump cam from #1 to #2 position might help but I think that I can be happy with this number since so many different changes never affected this spike. I wonder if a vacuum secondary unit drops to this level and this is a DP issue. I would rather be safe than sorry at the WOT transition.
I also lowered my in D idle A/F ratio from yesterdays 13.8 to 13.6. This engine really likes the 13.6 in D A/F reading. Even after changing the in D A/F reading, my cruise readings were still in the 14.0 to 15.4 range.
The current setup was very responsive in the light throttle reaction and the WOT transition. My 195 thermostat kept the engine temp right at straight up on my stock engine temp gauge.

I am sold on these wideband kits. The following is a review of where I started (Spring time) on the carb setup to this morning.
Spring: 66/75 jets, 8.5 HFPV, red/037 primary pump, red/031 secondary pump, .071 IAB's, .033 HSAB's, .028 IFR's.
This combo showed way too lean transition circuit and too rich main circuit cruise.

Current: 62/75 jets, 9.5 HFPV, black/037 primary pump, black/.018 secondary pump, .071 IAB's, .036 HSAB's, .031 IFR's. I would have never guessed that I could get away with 62 primary jets.

I am very pleased with the current tune of the engine especially in the high humidity this morning. Unless the 13.0 seams too lean at WOT, I think my only decision is whether to buy a second wideband for the passenger side of the engine or not.
Thank you very much for the responses as I have learned so much from everyone.

"The rich spike stayed in the 11.8 to 12.2 A/F range. The 62 jets did not hurt my WOT A/F number, it was still at 13.0 at my shift point. It also took away from my low end power at WOT."

Can you explain what you mean by "took away from"? Are you saying that the jet change to 62s reduced the low end power? Was the AFR different after the rich spike clears? I would think that the rich spike is definitely impact power on the initial transition to WOT.

If the smallest squirter doesn't tame the spike some, I wonder if increasing the AP clearance on the secondary side only might help slightly decrease the total pump volume and the discharge onset.

Dave

Y07_A66:

OK, looks like you posted an update while I was typing my last response. So the low end power change was due to the PV. Where you able to observe a difference in the low RPM AFR at WOT with the different PV in place?

" Do you think that the 13.0 is a safe WOT reading at the shift point? "

I have always heard that the typical motor will like somewhere between 12.8 and 13.2 at WOT. At this point, I think the only way to really refine the best WOT number would be on a chassis dyno or dragstrip. You are likely very close though, and only you can answer if further tweaking would be worth the effort. If you have screw-in PCVRs you could increase your WOT AFR without further disturbing your cruise setup.

With respect to a second wideband, here is something to consider. I have two bungs but only 1 wideband. I move the sensor from side to side periodically. This made some sense when I had a single plane manifold on it since one side of the carb will have more influence on one side of the motor but now with a dual plane, one side of the motor is already feed from both sides of the carb so it is hard to really know whether the motor wants a staggered jetting. Best bet is probably to check the plugs and see if all the plugs on one plane look the same or different from the other four.

I am very impressed with how well you have done with your tune. Well done!


Dave

Y07_A66:

I also meant to comment on this -

"I am wondering if delaying the secondary pump cam from #1 to #2 position might help"

The squirter experiment showed that delaying the fuel delivery is not having a positive effect. Clearly the issue is with too much volume. As I remember, using the #2 pump cam position increases the volume, in addition to delaying the start. This is not what you need.

Dave

Dave,

""As I remember, using the #2 pump cam position increases the volume, in addition to delaying the start. This is not what you need.""
- Good catch, you are correct.

""If the smallest squirter doesn't tame the spike some, I wonder if increasing the AP clearance on the secondary side only might help slightly decrease the total pump volume and the discharge onset.""
- BINGO!! I did not think of this before, but turning in the screw should do the trick. I will pull the black cam which has a more aggressive lobe up to about 50% travel than the pink cam, and put the pink cam in there with the additional clearance. Thanks!

""So the low end power change was due to the PV. Where you able to observe a difference in the low RPM AFR at WOT with the different PV in place?""

- Yes the change was definately from the HF power valve swap. In this carb, the two door pv did not have much response once the vacuum dropped below the rated level. As soon as the HF unit was back in, I could definately feel the difference. No, I did not observe the low end A/F ratio. I waited to watch once I got higher up in the rpm range.

I was thinking of adding one more jet size to the secondary side to see if that would bring the WOT A/F down into the high 12's. I might try that if I get bored. That would take my 75's to 76's.

Thanks allot for your help Dave.
Are you thinking of testing a high flow pv to help with your lean spot?

"thinking of adding one more jet size to the secondary side to see if that would bring the WOT A/F down into the high 12's."

Yes, that could be worthwhile. It is easier to try that, then mess with the PCVRs. One thing I think about on my motor is primary to secondary balance. I have been tuning my carb (unsuccessfully I might add!) with the secondaries disabled, so that the primary behavior can be directly observed. Most say that 8-10 jet sizes difference keeps a good balance (assuming PV up front, not in rear). You could add up the area of the mains+PCVR versus secondaries, although this is not exactly the same as flow. If you are a racer, it is something to consider. I don't see that going up one or two jet sizes is going to make your balance much different from what it is today.

"Are you thinking of testing a high flow pv to help with your lean spot? "

I do run a high flow PV. My lean spot is just off idle. I have been trading issues with an ugly rich highway cruise for an off idle lean stumble I can't get rid of. My carb (QFT 850-PV) was designed as a race carb and sold as a race carb, but I have been trying to get better street manners for my street/strip ride (mostly street). It's probably a bit foolish of me. The carb does not have very good low speed airflow behavior. I think I might have mentioned that at light throttle, there is a huge lean dip on a shift, and the carb takes a moment to recover good metering. I still need to get a looser converter (running a stock 440 unit right now), and that will make this less of an issue.

I had the car out this weekend, and sometime during the week I need to pull all the plugs to look for signs of oil. It seems the motor is running a little smoother, so I am again hopeful that I have solved that problem. Also found an ignition problem today (bad rotor) that was causing a slight miss. At the moment I changed the IFR/bleed/main jet combo to get good off idle and low speed operation, and good WOT AFR. The nasty highway (3K) cruise AFR is back, with the wild AFR swings with rich dips into the 11s. I wonder whether the mains are "spitting" fuel at 3K and 22" vacuum. I realize now that the mains are flowing some fuel under these conditions and I am again pondering the emulsification jets.

I'm open to suggestions if anyone has them!

Dave

""Most say that 8-10 jet sizes difference keeps a good balance (assuming PV up front, not in rear)""
- My carb setup came with a 14 jet spread front to back from Quick Fuel. My current jet spread is 13. I have noticed a .2 A/F change on the primaries with only a one jet size change. This carb is very sensitive.

I was looking back thru my charts and I found that this 11.8-12.2 A/F spike from cruise to WOT was not as bad of a problem when our outside temps were in the 60's-70's. I was getting A/F readings at the 12.5 A/F mark before the Summer heat hit. Maybe I just need a leaner cam adjustment during the Summer time.

""I wonder whether the mains are "spitting" fuel at 3K and 22" vacuum. I realize now that the mains are flowing some fuel under these conditions and I am again pondering the emulsification jets.""
- Have you tried delaying the mains to see if the problem moves up in the rpm range beyond your cruising speed?

"- Have you tried delaying the mains to see if the problem moves up in the rpm range beyond your cruising speed? "

I played with the MAB only a bit so far. At the time it appeared that smaller MAB helped. At the moment I have .031 in the primary down from .033. However, it makes sense to explore that again. Thanks for the thought!

Dave

Dave,
I took your suggestion about adding clearance to the secondary pump cam to try and lean out the 50/55mph-WOT rich spike.
Ref:
Was: 11.8/12.2 with WOT shift point at 13.0
Now: after a couple of times of shortening the secondary cam screw (larger gap), this worked great! I am now at 12.4/12.6 and my WOT shift point leaned out to 13.4 but a few jet sizes on the secondary side should fix this issue. I was concerned about not having the pump cam gap tight but it was very responsive to the gap. I have to say that it might be a touch quicker in response now at cruise to WOT.
I am going to delay it a little more and then get my WOT A/F around 12.8 or so, then I am going to play with the stop/WOT to see where it is at. I am one step closer!

Note:
I have been using the black cam on the secondaries since it is the smallest volume cam. I tested an .018" squirter and found that the 50-55mph to WOT A/F ratio went lean first (mid 14's) and then dipped to the previous 11.8. Now since I have the gap (apx 1/8") and with a .031" squirter, the A/F ratio goes straight into the 12's instead of going lean.
I think the tricky part will be tuning the idle to WOT tuning. This might require partial throttle then to WOT from a stop instead of 100% throttle from a stop with the DP style carb. But, with delaying the fuel on the secondary pump, I might be surprised.

Thanks a bunch Dave!

Y07_A66:

Fantastic! I'm glad loosening the secondary AP helped. It looks like you have a decent convertor in the car, so the standing start might not be any problem at all. Traction is likely to be the first problem you encounter with street radials!!

I didn't do anything on my car this week. The temps have been into the low 100s here, and it doesn't really make sense to try to tune under those conditions. Last weekend I had the car out when it was in the upper 90s, and the more I drove it, the more of a problem the off-idle stumble was (as the motor got heat soaked). Today it finally rained here, so no option for taking a spin. Hopefully it will be a little cooler next weekend.

Please keep us posted.

Dave

I have a small tuning issue that I am trying to decide how to fix.

I have my cruising A/F range between 14.5 and 15.5 below 65mph or so. When I am cruising and I let off of the pedal, the A/F drops down into the mid 13's. I am assuming that the vacuum goes up which pulls more fuel making it rich. How do I correct this?

I am currently running a distributor with out a vacuum advance canister. If I had a vacuum advance distributor, would this correct this issue?

Thanks

Y07,
It sounds to me like the transition circuit is still contributing to the overall AFR under those conditions. As you correctly observed, the AFR goes richer because of the high engine vacuum caused by letting off the gas. This pulls extra fuel out of the transition slots which makes the AFR richer.
One way of limiting it is to install restrictors in the transition circuit. But don't expect miracles, because the restictors can only do so much before they limit the fuel flow to the point of causing a bog. Another method is to find a baseplate with smaller transition slots.
Honestly, an AFR of 13:1 doesn't sound so bad to me. Many Holley carbs have AFRs in the 11-12's during deceleration.

Martin,
I am running on the transition circuit up to about 70mph with my current setup. I just assumed that mid 13's was rich. Thank you for your response.

UPDATE:
My last issue was the WOT shift point was showing 13.4 A/F with the 075 secondary jets and my 50/55-WOT rich spike was getting better at 12.4-12.6 after adding more gap at the secondary pump cam/arm.
I swapped out the 075's for some 078's and now my WOT A/F is good at 12.8 but my rich spike from 50/55-WOT came back rich around 11.8-12.0.
I will add some more gap at the secondary pump cam and see what happens.
I also tested a rolling start to WOT and found a 11.8 A/F spike reading at the rolling start and it leaned back out the the 12.8 mark at the shift point.
So back to leaning out the secondary pump. I am still wondering if swapping out the 40% secondary linkage to the 60% delay may help a touch.

This is my latest carb setup:
62/78 jets, black/037 & black/031 (+ gap), 9.5HFPV, N=1000rpms @ 14.5"hg & 13.0/13.2 A/F
D=900rpms @11.5"hg & 13.6/13.8 A/F
Notice how much richer the N idle is compared to the tranny being in D with the foot on the brake. I tune the idle in D so I let the N reading fall where it ends up.
30mph= 14.0 A/F
40mph= 14.6 A/F
45mph= 15.4 A/F
50mph= 15.0 A/F
WOT = 12.8 A/F

I have always noticed a lean jump at 45mph for several test drives now. It is usually my leanest cruise reading. I did not check it today but my 3500/4000rpm cruise has been in the 14.0-14.2 range with the 62 primary jets.

Back to secondary tuning.

Y07_A66:

"I am still wondering if swapping out the 40% secondary linkage to the 60% delay may help a touch."

I have never played with mods to the secondary linkage, so take what I say with a grain of salt. My understanding has been that the secondary opening progression tuning was for part-throttle racing such as road racing.

It seems you have a nice bag of tricks to get the WOT AFR were you want it. One more thing you may want to consider is decreasing the secondary MAB, instead of increasing the jet. You could go back to 75 or 76 jets, and try decreasing the MAB a few steps. This will change the slope of the fuel curve, and could be useful if the AFR is good at lower RPM but not where you want it at higher RPM.


Update on my problems: I tinkered some this weekend trying my smallest MAB (.025) and the largest (.035), just to see the effect. The big AFR swings were still present under all tests at highway speed. The smallest MAB moved the range of AFR lower (centered about 12.3) as expected, and the largest moved it up (centered about 13.1). At this point, I am thinking there is still some sort of an ignition problem, and the rich dips are the result of a miss. My wideband is a little slow, so it is hard to correlate what is shown on the meter with other sensory input. If I really focus it seems I can hear some subtle farts in the exhaust note at highway speed.

At first I thought it might have something to do with my 6AL-2, since highway speed (3K) is right when it drops the multi-spark. However I need to do more experiments to see if I can determine if it happens at a specific RPM or conditions. I haven't been able to notice anything at speeds in the 45-50MPH range. Any thoughts on what could cause a light throttle miss at higher RPM?

Dave

I am not sure about the 40% to 60% change either but it is an easy swap on the linkage.



""One more thing you may want to consider is decreasing the secondary MAB, instead of increasing the jet.""

I increased the size of the secondary MAB to keep my transition circuit active during my upper cruising speeds. My curve starts to go richer above 70mph so I want to keep the MAB's where they are. I don't mind the jet spread and I am giving it what it wants.
-----------------------------------------------

""Any thoughts on what could cause a light throttle miss at higher RPM?""

What conditions are your wires and distributor?
I wish that I could give you some help on this but I am not sure what to say.
Where did Jim go? Any ignition guys want to give this a try?

"increased the size of the secondary MAB to keep my transition circuit active during my upper cruising speeds."

I would have guessed that the secondaries are closed during high cruise conditions, but if not, the secondary linkage change you are considered would likely guarantee plenty of margin to not activating the secondaries during cruise conditions. Just something to keep in mind during further tinkering.

"What conditions are your wires and distributor?"

The wires are MSD 8.5 super conductor, and are about 2 years old with a little over 1000 miles on them. The distributor is from a MP electronic ignition conversion kit, and it probably 11 years old, but with less than about 3000 miles on it. The control box is a 1 year old MSD 6AL-2 (replaced a MP chrome box). Plugs are NGK 6's.

I have been wondering about the distributor. However, I have been hoping to retain the vacuum advance for later experimentation, and the aftermarket distributors I have looked at so far don't have that feature. My shopping criteria is easily adjusted mechanical advance, vacuum advance, compatibility with the 6AL, and use of stock style plug wire ends. I could change over the wires if I had to though.

The distributor has been disassembled lots of time, while I have been tinkering with the advance curve. I don't think I did anything bad to it, but I guess it could be something subtle. The reluctor gap has been checked multiple times and seems fine. One or two of the tines are a little bigger than the others (insert generic statement about quality here...), and I use those to set to the gap. The distributor did have a noticeable problem with rotor phasing but I corrected that by adding shims under the vacuum canister to reposition the advance plate.

I also have wondered whether JimG still visits here. I have not had as much time to visit this site either in the last month or two, but I can't remember seeing any recent posts from him. Hope he is just busy enjoying his ride!

Dave

Seondary Pump Tuning Results:
I have been chasing a 50-55mph to WOT rich spike (10.0 to 12.2 A/F spike) and I have finaly made some progress. I was also trying to tune my idle to WOT rich spike of 10.0 to 12.0 A/F which was making the car a dog off the line with the DP carb.
With my backup DP on the shelf, I started playing with the secondary pump/cams/arm trying to limit the fuel from the secondary side to try and limit the rich spike. After grinding down a black cam, I noticed the A/F spike getting leaner but not nearly enough. Then I added an air gap at the black cam and pump arm screw and it got a little better. So I knew if I could limit the secondary side more then I should see the results.
Then I grabbed a pink cam which has a very slow lobe and I rotated the cam CCW as far is it would go to get the least amount of fuel from the secondary side as possible at WOT. I was not sure that it would work because it did not produce much of a pump shot at WOT.
So I went out this morning for a test drive and I am so suprised at the result. Limiting the secondary side of the DP gave me instant tire spin from idle to WOT. Of course I wanted to test this over and over and over again to make sure but after several idle to 100% WOT shots, it was immediate tire spin each time. My idle to 100% WOT A/F showed an immediate lean spike to 16.0 but the tires still spun like mad. The 16.0 spike then richens up very quickly to about 14.2 during the tire spin and then drops down into the 13's as the mph comes up. The lean spike does not appear to hurt the performance but I am going to test a larger primary pump cam to see if this helps. The larger primary cam will also help my light throttle A/F which is now into the 15's with the cooler weather. The warmer afternoon temps may show a richer A/F too.
Note: this was with the secondary linkage set at 60% delay.
Then I tested my 50mph to WOT rich spike and I was again surprised. My rich spike is now at 12.4/12.6 right where I was hoping. After a 50mph to WOT run, the rich spike starts at 12.4/12.6 then then slowly rises to the 12.8 WOT shift point.
Then I tested idle to WOT thru both shift points and they both showed 12.8. I am very pleased!!
I am very surprised at the idle to WOT response since the secondary cam has been delayed.

I suspected you would be reaching the point of pondering the topic of traction.....

The lean spike on idle->WOT is pretty high, and wonder whether it should be tamed some. I would suspect that with really good traction, the motor would bog.

Do your comments about being surprised by the results imply that the car would not have as much tire spin with a lower AFR on the WOT hit?

Dave

""The lean spike on idle->WOT is pretty high""
- Yes it is and I am already working on that one with a larger squirter on the secondary. If that does not fix it then I am going to change the secondary linkage from 60% to 40% to see if that helps. I just don't want to change the volume.

""Do your comments about being surprised by the results imply that the car would not have as much tire spin with a lower AFR on the WOT hit?""
I have beeen fighting an over-rich Idle to WOT A/F reading which made the car a dog. I have read where others were having great response at idle to WOT with their DP's but I was having to raise the rpms a little bit to see the same results. Now it is instant tire spin with the delay in fuel from the secondary pump.