The last one in your list matches the cover. copyright 1987

The section I was refering to is titled "Road-race Tuning" on p. 123
- in it it suggests 30 or 40 mph to 80 mph, and specificly to crowd the vacuum readings down to the PV opening. This is to get the best main jets.
It follows a section titled "special Procedures for 'Wild' Camshafts. That section has diagrams showing the proper transfer slot to throttle relationship.
The chapter is titled Carburetor & Performance. There's a drawing of a 413 long cross ram in cut-away view on the chapters first page. Very cool picture.

(I also have the little 4150 book but its redundent to the big book. I keep the little one in the garage for reference.)

I decided to leave the HSAB's alone and just change the secondary jetting to get my 50mph-WOT number richer than my previous 13.0 A/F. I swapped my #80's for some #82's and then my 50mph-WOT A/F ratio went down to 12.2-12.6 to the shift point. Then I wanted to test what would happen if I lowered the rear float only by 1/4 turn and that chage made the same 50mph-WOT A/F go to 12.4-12.8. So it appears that using the rear float can "tweak" in the WOT a/f number if needed.
I then decided to lower the primary float by 1/4 turn and it leaned out my cruise A/F by about .4 points on the gauge. This is where I ended up after several drives today in 75 temps.
D (foot on brake) = 13.2-13.4 (this number can go as lean at 13.6-13.8 before I start to have idle issues)
30mph = 14.0
40mph = 14.6
50mph = 14.8-15.0
60mph = 14.6-14.8
50-WOT shift point = 12.6-12.8
I achieved the above cruising numbers with 60 main jets, .060" iab's, .031" ifr's, and .039" hsab's.

I did find that the 50mph-WOT felt quicker with the A/F ratio in the 12.6-12.8 range than it did in the richer 12.2-12.4 range. The half a point was felt in my seat.

My primary cam/squirter is good with a Red/.042" combo. This gives me a smoooooth light throttle take off from a stop to cruise in the 13.8-14.2 A/F range. This combo also helps keep my medium throttle A/F into the 13.5-14.0 range which feels strong. This is with a 10.5 high flow power valve, .069" pvcr's, and small #60 main jets.

Now I am testing my secondary cam position and linkage delay (40% or 60% delay for the mechanical secondaries). Like last Summer, I have found that adding an "air gap" on the secondary pump linkage (between cam and bolt) helped lean out the WOT stabs at lower speeds. I started out with a 11.0 A/F reading from idle to WOT and now I am down to a 12.0 reading by increasing the gap which limits the extra fuel of the secondary pump. I have a couple more tests to run (enlarging the gap about one full turn at a time) before finishing my pump cam testing. Making this "air gap" did affect my 50mph-WOT reaction but adding a larger squirter on the secondary pump fixed that issue.
I now know that for my setup, that my in D A/F, my cruising A/F, and my WOT A/F numbers are close enough to leave alone. Now for the timing of the secondaries.
I have learned that just 1/4 turn on either float and 1/12 of a turn on each metering screw can affect the A/F ratio by .4/.6 on the gauge.

For those of you who are thinking of getting an O/2 sensor for your carb tuning, I can't think of a better tool that you can buy. They sure help show where you have been and where to go next on your tuning.
I started this thread with the idea of learning what each change can do to the state of tune. I had no idea how involved this thread would get after a year of tuning. This shows that even a DP carb can be tuned to work well on the street. I look back and kick myself for not getting an O2 sensor earlier.

Frederick,
""things just happen too fast""

EXACTLY!! When you watch the linkage on the carb go from a steady cruising position to WOT, the secondary linkage moves so fast that the air gap is taken up in a flash. With the correct secondary squirter, I can not feel any hesitation at all with a large air gap.

I am currently testing the secondaries with the pink cam which has a very slow ramp speed (& medium sized volume) and I am using a .048 squirter on the secondary side to help speed that back up. If I was to use a quicker ramp speed cam (maybe a black), then the squirter will prabably be smaller. What I am trying to achieve is to lessen the amount of pump shot given by the secondary cam to lessen my idle-WOT A/F and my cruise-WOT A/F rich spike that I currently have without screwing up my other A/F readings. Since my cruise and my WOT A/F's are very close, I know by the A/F gauge that the secondary cam is giving too much extra fuel when I go to WOT.

Since I know that the pink secondary pump cam is too much volume, I could use a smaller pump cam or just shorten the adjusting bolt to create this air gap on the pink cam. The overall amount of the pump cam is reduced with the air gap (shorten the bolt) and since I had a slight hesitation at 50-WOT with a .037" squirter, I changed the .037" to a .040" to get rid of the hesitation. Since the pump cam is just a "band-aid", that is all that I am using it for. I do not need the entire pink cam's volume, so I am going to make the air gap larger by one full turn and retest. Then if that is still to much volume, then I will make the air gap larger by one more turn and retest again. Then if I run out of bolt adjustment, I will drop down to the smallest pump cam and retest. I did this several times last year and I have charted some of the changes. Since I made some ignition changes over the Winter, I am now just re-tweaking the rear pump cam to finish the tuning process.


I agree that the .042" primary squirter "seems" huge but I am using one of the smaller pump cams (red) and the Red/.042" combo keeps my acceleration A/F numbers in the range that I want. The squirter just speeds up or slows down the volume created by the pump cam. Since I do not want to increase the overall volume of the primary pump cam, I just want to adjust the speed of it by using a larger squirter until my A/F numbers are where I want them for accel. If I was using the stock #68 primary jets, then I would guess that I would be able to use a much smaller primary squirter. But since I have dropped my main jets from the stock #68 to now #60's, and I am able to use a smaller red pump cam, then I need the larger squirters to help tune the speed. I am running 30 of timing at idle. This might be some of the reason that a .042" primary squirter gives me a better A/F than a .037" primary squirter on light - medium accel.

I have found that since I have done so much tuning on the other circuits, that now I am down to just juggling the secondary cam and squirter to keep my A/F in check. The .042" squirter is not what "everyone else" is running, but neither are #60 primary jets. This is exactly why these O/2 sensors are such a great tuning tool.

I now totally understand why some people say "do not use a DP carb on an auto car on the street". They can be a bear to get the mechanical secondaries tuned. But I can now see exactly what my A/F is doing from idle-WOT and from cruise-WOT and I can correct the amount of fuel that the secondaries are adding which is causing my rich A/F spikes at WOT situations. I have found that in my case, limiting the secondary pump cam volume is the key.
Is "everyone" tuning their DP like this? NOPE!! Can "everyone" running a DP see what I am seeing? NOPE!!

Thanks for the response and get that new float installed!

I now see what you're trying to accomplish; less volume.

WOT may be fine with the smaller pump shot, but doesn't the air-gap give hesitation on less than wide-open throttle?
Just seems the opposite of what you want, no pump shot when you most need it; when the mains aren't flowing yet.
Have you thought about shaping a cam to you needs?

Quote:

---

I agree that the .042" primary squirter "seems" huge but I am using one of the smaller pump cams (red) and the Red/.042" combo keeps my acceleration A/F numbers in the range that I want.

---

Are you sure you're tuning the right circuit. I'm not sure you can judge the pump shot on a gauge.
From what I know the shot doesn't last more than a second or so.
With the engine off and looking down the throat, you should be able to see how long a WOT pump shot actually takes?

I'm sure you've seen this one?

This is the correct one, according to tuner.

Negative on the float
I did take the car for a spin on Saturday and Sunday.
Everything fine on Saturday, but on Sunday the AFRs were much leaner, right from starting?
Went from the normal 13.5 to 15.
Any idea? Blocked jet perhaps?

Are you saying after sitting overnight, the same driving condition read leaner on the meter?
If so, gasket sealing is my first guess, metering block to body.

""From what I know the shot doesn't last more than a second or so.""

That is the chart that I use. Per the chart, the pump cam can deliver fuel UP TO 50% or UP TO 80% throttle. At WOT, I am not sure how long the shot would last (in seconds pending on the pump cam).

Have you tested between the 40% secondary delay and the 60% secondary delay? If so, what have you noticed?
I have been going back and fourth between the two and I am still not sure which one to do my final tuning with. It may depend on the outside temps. Maybe using the 40% in the cooler temps and then using the 60% delay in the Summer months.

Last year I tested allot with the 60% delay and found it good for casual cruising. I am now testing the 40% delay and it appears to be a bit more aggressive which makes sense.

Last year, I was testing the "air gap" on the secondary pump cam and it actually worked great with the 60% delay linkage. Last year, I was also using a non-vacuum advance distributor which gave me 34 degrees total timing. I started out a couple of weeks ago trying to use the same "air gap" on the secondary side but this year I added a vacuum advance distributor which gives me more time from idle and up. I have not been able to make the "air gap" work so I have gone back to the standard gap setting. I think that the extra cruise timing this year has made the biggest setup change.

So far, I have been testing with the 40% linkage and I am swapping around the pump cams to see what works best. The extra timing is making me go with larger pump cams this year. My initial timing from last year was 24 degrees and now with the manifold vacuum advance setup, I now have 32 degrees timing at the same rpm. So this is wanting a little more cam on the front side. Now I am trying to select the correct rear pump cam and the interesting thing is that I am seeing an A/F change on the meter with the different size pump cams at accel and especially at WOT. I am now trying to get my light acceleration A/F down in the 13.6-14.0 range and then get my medium acceleration A/F in the low 13's and before the pump cam swaps, my WOT was 12.4-12.6. Last night after some larger pump cam changes, my WOT A/F spiked into the 11's. So I will keep adding to the P side and then reduce the cam on the S side to try and get my WOT numbers back into the 12's while richening up the accel A/F numbers.
Note: When my accel A/F numbers were in the high 13's to low 14's, the accel power was down. Now that I am approaching the mid to low 13's under different accel conditions, the car definitely feels much more responsive.

Y07_A66:

It makes sense to me that the acc pump shot will need to be quite different between the 40% and 60% progressive linkage settings. The amount of additional airflow when the secondaries first open will be different on a percentage basis between these two cases. With the 60% linkage it appears that the initial crack of the secondaries did not cause a significant lean hole before the secondaries mains starting flowing since the additional CFM was a small percentage of the total CFM. With the 40% linkage, this transition happens at lower total airflow thru the carb and therefore the impact of the secondaries opening is bigger.

That's my theory at least!

Dave,
Thanks for explaining that. I wasn't coming up with any good reason for such a difference except maybe the extra timing at cruise. Your description makes allot of sense. Once I added more fuel to the secondary pump with the 40% delay, the throttle response increased allot as the seconds started in. (I was previously using the pink cam with the "air gap", then I added the red pump cam with standard gap for more fuel.)

Thanks allot for the reply.

I now have my cruising A/F numbers from 14.0-14.8 (40mph-70mph). I found that it was surging a little bit at 45-50mph at the previous 15.2, so I richened up the front float just a touch. I think for now on I need to keep my cruising A/F in the 14's.

I also have my pump cams/squirters close. I was using red/042 on the P side and red/040 on the secondary side but at 50-WOT, it gave me a rich spike at 11.8 or so. I was still only showing about 13.5 or so under a strong accel, so I wanted to richen up the Pside just a bit.
I am now running orange/037 on the P and the smallest black/031 on the secondary. This combo was VERY close to what I am looking for. My light accel was very smooth from a stop and it showed 13.8-14.0 under very light take off and no hesitation. I was showing mid to high 13's under medium accel and 12.8-13.4 under aggressive accel (not WOT) with the pv open. I also tried a rolling start (around 15mph to WOT) and the A/F dipped to the 12.4 again and hit 12.8 at the WOT shift point. My 50mph-WOT spike is 12.4 and it leans to the 12.8 mark at the shift point.

I am very happy with how the car runs today. All of my A/F numbers are in and the "Seat-of-the-pants" is fun all around. Now I am going to try and get some cruising miles on it.

EDIT:

I do have a lean spot at cruise when I go to a medium accel. My A/F goes from the low 14's to 16 then back down to the low 14's. This must be from when the secondaries are opening with the BLACK/031 cam/squirter combo. I am going to test a 037 squirter to see if that fixes the lean spot.

My next test will be to see what A/F numbers I have from idle in D (with foot on the brake, like at a stop light) to WOT with the DP carb.

Then I am going to try to see if I can switch from 91 octane to 89 octane once I have everything dialed in.

Excellent! Thanks for continuing to update this thread.

""I do have a lean spot at cruise when I go to a medium accel. My A/F goes from the low 14's to 16 then back down to the low 14's. This must be from when the secondaries are opening with the BLACK/031 cam/squirter combo. I am going to test a 037 squirter to see if that fixes the lean spot.""

I have been chasing this lean spot and I found something that I did not know. This lean spot is when I am cruising about 50mph or so and then I slowly apply pressure to the pedal. I keep adding pressure until I get up to about 70mph or so. The gauge stays in the 14 range (which is my current 40mph-70mph cruise reading) and then the gauge jumps to 16 for a second and then comes back down into the low 14's again. Since my secondary linkage is setup with the 40% delay, I was first thinking that when the secondaries come in, then I am getting the lean spike to 16 until the secondary circuit catch's up to return the A/F back down to the 14's. But now after some testing I am not sure. I started out with the secondary pump cam/squirter at black/037. Then I swapped in a .047" squirter and had the same A/F lean spike into the 16 range. Then I swapped out the black pump cam (smallest cc) for the white pump cam and kept the .047 squirter and I had the same lean spike into the 16 range. Then I jumped up to the orange cam and I still had the lean spike. Apparently the lean spike might be on the primary side instead of the secondary side. So I will swap the squirter on the P side to see if this helps.
But what I learned thru all of the cam swaps today was with each pump cam swap on the secondary side, my 50mph to WOT A/F reading stayed at 12.4 and leaned to 12.8 at my shift point. Even though each cam has a larger cc rating (black, then white, then orange), the cam size did not affect the overall A/F reading at WOT. I though for sure that I would have seen an A/F change after each cam swap. The outside temps only changed by 2 degrees during the swaps so the weather did not affect the outcome.
The overall A/F was not affected by the cam swaps but the performance (seat of the pants) was definately felt. The black cam was a little lazy when the secondaries kicked in under medium to heavy accel. Then the next larger cam I tried was the white cam. This cam brought in the power a little better over the black cam. Then I moved up in cam size again to the orange cam. This cam really woke up the motor when the secondaries kicked in. The orange cam made a big difference in performance over the little black cam from a rolling start to my 50-WOT acceleration.
So even though I felt the performance difference from the black cam to the orange cam on the secondary side, my WOT A/F number did not change.
EDIT:
The weather changed by 20 degrees and I upsized both sets of squirters and now I am seeing an A/F change with both orange cams. In the hotter weather, the orange cams are sending my idle to WOT into the 11's along with my 50-WOT A/F into the 11's. So my previous statement did not work for the cooler months but the cams sure start affecting it in the warmer temps.

This lean spike might also be when the carb is transferring from the transition circuit to the main circuit. So I might have to look at the front pump cam/squirter for some help, or richen my HSAB's up a tad to start the mains a little earlier.

I have been doing some WOT tests and after several attempts to find what my combo likes, I now know the answer.
Since this is a street car, I decided to make all of my WOT attempts from a steady 50mph cruising speed (14.2 A/F) and let the car go thru the first shift point which is 5800rpms. Then I write down what the richest spike is right when I go to the floor with the pedal (DP carb) and then I also take notes on what the A/F reading at that WOT shift point.
Note: All of these tests were taken with the outside temps between 75-85 degrees.

I started out with 82 rear jets and I was getting rich spikes into the high 11's with the 50mph cruise to WOT A/F showing 12.2-12.4. I ran this way for several weeks and the car felt good at WOT but not great. The car was also showing low 11 spikes at a stop to WOT too which is waaay rich with my auto/3500rpm flash/3:91/27" tire setup.
I then lowered the rear float and got the WOT A/F showing 12.4/12.6 with spikes still in the high 11's. The car felt about the same so I wanted to lean it out again.
I then swapped out the rear jets from 82's to 80's and then reajusted the rear float to achieve 12.8 A/F at WOT and what a huge performance response this gave. My WOT spikes were in the 12.4 range while the WOT shift point was at 12.8 at both WOT shifts. My idle to WOT response was excellent with my spike around the 12.0-12.2 range. This was my best WOT setup to date.
I still wanted to test a leaner WOT A/F so I swapped out my 80 rear jets for 78's and then adjusted my rear float to achieve a 13.0-13.2 WOT A/F reading. This felt good but I could tell that the power faded, but I did not hear any detonation.
I then lowered my rear float again and got a 13.2-13.4 WOT A/F reading and the power went down. My idle to WOT reaction was not as good and my overall performance went down and I started hearing detonation at hard throttle and WOT.
So after testing my rich WOT number (12.2 A/F) and then my lean WOT limit (13.4 A/F), I have now rejetted to go back to the 12.8 WOT A/F number. This is leaner than a chart that I have for 10%E (12.2), but I have found what the best performing A/F needs to be for my combo.

All of my testing has been done with one FAST #170634 A/F sensor kit on the drivers side exhaust header collector. I have now talked myself into a second A/F sensor kit to start looking at the passenger side numbers. I could have just moved the existing sensor to the passenger side, but I want to beat myself to death by added a second sensor and see how close I can get both sides to read. They should both be close but I know from my experience that a small movement in one metering screw can sure make the A/F gauge move. Since I have one side of the carb setup per the gauge and I only "eye-ball" the second side, and I also found the rear passenger side header hotter than the front of that same header, I want to add the second sensor to dial in the idle A/F and also see what I need to do to get the header exhaust temps closer to each other on the passenger side.

I just wanted to give an update for those who need a reference.

I bought a second FAST analog O/2 kit for the passenger side exhaust. (My exhaust is setup as true duals with no crossovers.)
I found that even though I marked all four metering screws in the full inward position (12 o'clock position with permanent marker), and I backed them all out the same amount, and I used the drivers side sensor as a reference. Even though I setup the passenger side the same as the drivers side (existing O/2 sensor), the idle was different from drivers side to passenger side once I had the dual O/2 sensors installed. This surprised me because even though I had both sides set the same, that the passenger side gauge was now showing about .4/.5 difference in the readings. It didn't take long to have both gauges reading the same, but the metering screws are different from the drivers side to the passenger side to achieve the same reading (within .2 on the gauge).
Another thing that I found was that when adjusting the passenger side metering screws, they mainly affected the passenger side O/2 sensor, but they still affected the drivers side O/2 sensor too. It took a few tries to get both sides balanced out, then I took the car for a drive. Overall, the two gauges were within .2 of each other with the carb setup the same from side to side, except for the metering screws. Cruise and WOT were also within the .2 or so which is close enough for me.
So after adding the second O/2 sensor, the main surprise was that setting the drivers side metering screws exactly the same from side to side did not show the same reading on the gauges. But cruising and WOT were mainly the same (passenger side was always .2-.4 leaner with the carb setup the same side to side). If I get enough energy, I might try adding slightly richer IAB's on the passenger side just to see if that brings in the passenger side O/2 reading at cruise a little closer to the drivers side.
The attached picture shows the difference at idle in P before I shut off the car for reference.

I've been playing around with an Innovate MTX-L gauge in my daily '73 Dart for a couple of months now. It's great fun being able to 'see' what's happening inside the combustion chambers.

Only difference is my car runs on Propane/LPG.

I've learned a lot aswell, but mainly how to tune a simple IMPCO propane system where the main tuning items are only a mixture screw and max-power screw on the LPG-mixer.
A lot of factors play a significant role in mixture-quality, especially with propane. As propane expands when heated, it also increases in pressure but mainly when it's a liquid state. When it's heated as a vapour under a controlled pressure/vacuum, it will lean out. Temp-differences with propane play havoc with your tune.
But with playing around with different springs in the propane vaporiser and the mixer, I've achieved a (I think) a very good tune now.


Pic below shows an AFR-number while idling from a while back.
The engine currently idles with an AFR of around 17 when warmed up.

PROPANE! That is cool. Thanks for sharing.

Now that I have had some more time with the twin O2 sensors, I have found that my idling in N, idling in D, and my cruise A/F readings from one side to the other are fairly the same now after a few adjustments. The passenger side usually runs about .2-.3 "leaner" during the above and I am good with that.
My current issue is that I have found my WOT readings from side to side are farther off than my idle/cruise numbers. My drivers side is right at 12.6 (aiming for 12.8) at WOT but my passenger side is richer at 12.2. I tested three different times from 50-WOT and a rolling start to WOT and my passenger reading is always .4-.5 richer at WOT.
My only tuning guess is to lean out the "passenger secondary main jet" by two sizes to see what happens. This means stagger jetting the rears.
Any other suggestions before I try this?

EDIT: http://www.popularhotrodding.com/tech/04...tech/index.html

I have now found two articles that show that the RPM intake required staggered jetting on the drivers side front corner and the passenger rear corner by 2 jet sizes. Reference #6 in the article for the diagram. The other article mentioned any four corner idle carb.

Thanks

Y07_A66
Do you have any results from trying your staggered jetting? I'm curious and have been following your thread for quite some time. I have about the same set up except my carb is a SS750 quick fuel stock jetting it came with 74 primaries and 80 secondaries and I also am using the same gauge as you but I have my sensor mounted in the Y part of my exhaust. I'm curious what your reading is at a steady cruising speed down the highway around 65 to 70 miles an hour. I'm running right now at about 13.5 to 13.8 and at idle my reading is 13.9 to 14.2. My jetting is set at 69 primary and 76 secondary. Keep up the great updates. Thanks
Pat Faley
67 Notch back Barracuda
408 stroker 4-speed
Peoria IL

Hello Fuzz,

When I started out, my goal was to get my 40-70mph cruising in the 14.6-15.4 range and my in D idle A/F appeared to be good in the 13-2-13.4 range. I am now running my 40-70mph (70 = 3400rpms) cruise in the 14.0-14.4 (.039" HSAB's, & .033" IFR's) range and my in D idle at 13.8-14.0 (.060" IAB's). These numbers are based on 10% E and 91 octane.

My main jetting is now 62's and my secondary jetting is now 74 (passenger) and 80 (drivers). The 62 main jets still show 14.0 at 4000rpms, so I know that my mains are in good shape. Note: both A/F sensors are within 0-.2 of each other during cruise conditions.
As of last weekend, my D side WOT is 12.8/13.0 and my P side WOT is 12.6/12.8. I just made a secondary float change this week to try and get the D side down to at least 12.8 at the leanest reading.

It appears by your part number that you have the downleg boosters which might be why you and I are so far apart on primary jetting, along with the engine size difference. But as long as the A/F is where you need it, then I say give it what it wants.

Have you messed much with the adjustable secondary linkage? I have tried both the 40% and the 60% and I like the 40% better so far.

Are you having any issues at a steady cruise then slowly accelerating creating A/F swings?

Are you able to control the rich spike when transitioning from cruising speed to WOT with your DP?

How is your cold start now that your in D A/F is leaned out to 14?

Thanks Fuzz