UPDATE:

I fixed my 50mph-WOT throttle lean spike with a larger squirter on the secondary side. Now I have no lean spike at idle to WOT (which was spiking to 16.0) or 50mph-WOT (which was also spiking16.0). Now my A/F goes richer as soon as I hit WOT.
I need help on this next one. I ran into this ealier into this thread but now I am ready to fix it. My A/F ratio from 60mph (apx 3100rpms) up to 4000rpms is too rich for my liking (14.0-14.4). So I tried to lean out the HSAB's to lean it out. I tested with my .036's and then swapped in .039's with no change at all in A/F reading in this range.
I am guessing that I need to lower the front jets a couple and see if that helps it out. This is my latest A/F readings taken on the same day but one was at 75 degrees and the other at 92 degrees.
Note: I was having cruising readings at 40-45mph at the 15.5 range so I wanted to richen that up just a bit and I swapped my .067 IAB's for a set of .064's and that richened up my cruise quite a bit. But for now I am going to just lower my floats a tad and recheck my readings.
75 deg (.036 HSAB's, .067 IAB's, "D" A/F=13.6-13.8 & solid idle)
30mph=14.0, 40mph=14.2, 45mph=14.4, 50mph=14.8
55mph= 14.8, 60mph=14.4, 3500rpms=14.4, 4000rpms=14.0.
92 deg (.039 HSAB's, .064 IAB's, "D" A/F=14.0-14.2 & rough idle)
25mph=13.6, 30mph=14.2, 35mph=13.8, 40mph=14.2, 45mph=14.4, 50mph=14.6, 55mph=14.6, 3500rpms=14.0, 4000rpms=14.0.
So you can see I need to lean out the cruise just a tad (lowered floats) and then I need to lean out my 3100-4000rpm range with what I am guessing a primary jet change.
Let me know what you think.

Something that I have noticed is that my in D idle A/F is richer than what I have read on the net. When I have my in "D" A/F set at 14-14.2, the idle gets rougher and my vacuum drops. But if I have it set in the 13.4-13.6 range, the vacuum is solid and it idles smooth.

Thanks

Y07_A66:

Your setup is pretty darn good!

A primary main jet change may help but be careful of creating a lean "hole" at part throttle before the PV opens. At cruise there is not that much fuel flowing thru the mains, but at part throttle there can be much more flow. A change which provides a small improvement at cruise may end up being too big of a change in the wrong direction under part throttle.

Another thought to consider is to try using your vacuum advance. This should provide for a smaller throttle opening at the same cruise RPM, and therefore move the slight rich dip up in the RPM band a little more. If the mechanical advance has been tweaked, the vacuum advance may also need to be limited.

I would not worry about the idle AFR that much; the engine is telling you what it wants. Optimal tunes are never "one size fits all". In addition to all of the variables in the engine (cam specs, exhaust sizing, intake manifold type, carb characteristics, etc), there is also the variable of how much load the converter is placing on the motor, and what sort of torque the motor makes at idle. In setup's like yours (and mine) a moderately rich idle is typical (IMHO).

Dave

""A change which provides a small improvement at cruise may end up being too big of a change in the wrong direction under part throttle.""

That is what I am afraid of. I am so close that I can make a small change and my A/F cruising numbers will be:
A) in the mid 14's to mid 15's
Or
B) in the lower 14's to the low 15's

So I keep going back and forth trying to decide what cruising range(30mph-60mph)I want to be in. Right now I am comfortable in the "A" range.

I have most of my setup figured out (jetting, pv,cams/squirters and bleeds) and I am just playing with the 40% and 60% delay on the secondary linkage and the float adjustment. The float adjustment can really dial in the cruising A/F without having to change any bleeds. I am going to leave my A/F at 3500rpm and 4000rpm at the 14-14.2 mark for now.

Over the long weekend, I was lucky enough to drive the car with the same setup in 60 degree, 75 degree, and 92 degree outside temps and the only change that I made was with the in "D" A/F adjustment. I was able to keep the cruise A/F between 14.2 and 15.6 as long as I keep the in "D" A/F between 13.4-13.8 and it drives great within those outside temps if I keep the in "D" A/F in that range. If I did not keep "D" A/F in that range, then the cruise A/F range would go leaner or richer than the 14.2-15.6 range which I do not want.
A Vacuum advance distributor might be in my future but probably not before Winter.

I am probably going to stop updating this thread because I am so close on the setup. I have learned allot from the information that a wideband can give and also from the responses from this thread. I want to that you again and to everyone else for your help.

Yes, I think you have your carb setup as good as could possibly be expected.

If you do try a vacuum advance distributor in the future remember to check the rotor phasing. I recently put a new MP unit into my motor, and it needed significant correction to the phasing.

This has been a great thread, and thanks again for posting all of the detailed results along the way!

Dave

I need some more help.
My last issue was having a cruising A/F ratio of 14.0 at 3500-4000rpms. I changed my primary jetting from 62's down to 60's and now I am seeing 14.4 at both cruising rpms. I can be happy with this for now. After discussing this issue with QF, the tech thought that it was strange having 62 jets in the primary side and still getting a rich number of 14.0. But after a long discussion about my A/F numbers (cruise, WOT, bleeds, etc.), it was decided to test the 60 main jets. That appears to be working.
Now I have created another issue. At any cruising speed (30mph-60mph) and I press the accel pedal for light to medium accel, my A/F goes lean (16.o+) and the car is surging under these accel conditions. What I have noticed is that once the vacuum drops below my pv rating (9.5 high flow), that is when the A/F goes into the 16.0+ range. Since I have leaned down the main circuit to the 60 jet, I am assuming that the pv does not have the flow to keep the engine happy now. This to me sounds like a PVCR issue (too lean) but I do not know anything about them except that they supply the fuel to the pv when the pv is open. I do not know what the stock PVCR's are in the SS-750-AN carb, but I am assuming that I need to open them up.
The following is my setup and A/F number as of this morning. As you can see, I am very close all over the range and I do not want to make a change that will affect the rest. I do know that I have a little bit to spare at WOT and my in D A/F was rich this morning at 13.0.
60/78 jets (stock spread was 14 sizes), .064 IAB;s, .039 HSAB's, 9.5HFPV, 40% linkage delay on secondary side, front float at 1/2 mark and secondary float at bottom of glass. (cool weather at 63 degrees):

35mph=14.6
40mph=14.4
45mph=14.8
50mph=15.0
55mph=15.2
60mph=14.6 (3100rpms)
3500rpms=14.4 (was 14.0 w/62 jets)
4000rpms=14.4 (was 14.0 w/62 jets)
0-WOT thru shift points: 13.0/13.0
50-WOT was 13.8 at shift point (lean)
50-WOT showed "0" on vacuum gauge with the 750 DP (actual 735cfms per QF)

If my PVCR's got richer, this might help the WOT number too with no other changes.
Is the PVCR the next change?

I am thinking of dropping the main jetting again to 58's and then sizing the PVCR's from that. This might lean out my 3500-4000rpm A/F into the mid to upper 14's. Then resizing my secondary jetting to suit. This might reduce the front/back jetting spread to get me a little closer to the stock 14 jet spread.
QF did say that the annular booster pulls more fuel than a downleg, but my jetting surprised him.

Thanks again.

I'm not sure I can help since I don't know much about the carb that you are working with. It sounds like you only have a PV on the primary side? If so, you might consider adding one on the secondard side also. For the type of driving that you are doing a PV on both sides would be the best setup.

Are the metering blocks fully adjustable? If so, when you remove the PV there will be two jets under there that can be changed. I posted a picture earlier of a billet metering block with jets in all circuits. The fully adjustable metering blocks make this kind of work much easier.

One minor point, the PVCR add fuel to the main well when the PV opens. So it basically just adds jet size when the PV opens. You can figure it out with some simple math. A 60 main jet plus a 30 PVCR gives you a 67 jet for example.

Another thing that you should do at this stage is to double check your measurements. Get another wide band sensor and swap it in and double check your numbers. You are making a lot of assumptions based on your measurements. Double check your measurement equipment before you go to far. You might be shocked at what you find out.

I've tuned myself into a corner a bunch of times and then found out that my measurement equipment was bogus and my tune was way off.

Andy,
The metering blocks are fully adjustable and I will be pulling the PVCR's later today to confirm the size. My current rear block does not have a pv provision though.
Can you give me the formula for figuring the main jet and the PVCR total jet size?
I am going to pull a couple of plugs on the side where the sensor is on to see what the plugs look like. I pulled a couple about four weeks ago and they looked real good.

Thanks Andy.

I do not know the exact diameter of my current PVCR's but they are in between .037" (sloppy) and .062". These were the closest drill bits that I had. The .062 was closer in size.

When opening these up, how much do you open them up when testing (.001", .005", etc.)
Thanks

For this type of tuning you'll want to invest in a set of pin gauges. They are fairly cheap for a small set.

I'd highly recommend buying a new metering block for the secondardy side that has a PV. Does your carb have four corner idle? That is another handy tuning device.

If you are going to drill the PVCR then you'll need to buy a set of small drills and a pin vise drill. (You'll do that once and then you'll decide to buy an adjustable metering block!)

Fully adjustable metering blocks aren't very expensive. BLP has them as well as all of the jets that you need.

I just pulled #3 and #7 plugs and they both were very similar. The porcelain was clear with slight brown color. Both of the plugs had a full ring of color on the bottom of the plug thread. They both looked good.
I do have fully adjustable metering blocks. I also have the small chuck with a small assortment of smaller drill bits for my air bleeds and my IFR's. But I do not have any precision bits for the PCVR's (.050's-.060's or so).
Can you give me some information as to why I should be looking at a pv in the secondary side of the carb? How do I choose the pv for the secondary side?

Thanks

nothin to add YET just savin the thread

I found the formula for tuning the PVCR's.
Take the stock jet diamter and the stock PVCR diameter, (2) each = 4:
3.1415 x jet x pvcr /4 = total area
Then take your new jet size x new pvcr until the new combo equals the area of the original combo.
Ref: 3.1415 x .068" original jet, .058" original pvcr = 003"
Ref: 3.1415 x .058" new jet, .069" new pvcr = .003"

I need to get me some more drill bits.

Using the new smaller main jet will allow me to lean out the primary A/F ratio (currently at 14.4) at the 3500-4000rpms range. Then by using the corrected pvcr's (larger) will allow me to tune the A/F of the fuel delivered by the pv to get me back into the 14 range (currently 16+). Then I will need to rejet my secondaries to get my WOT corrected to the 12.8/13.0 range.

Hi Dave,

You posted on my thread on dodgecharger.com, thanks again for the advice.

I have measured the PVCR, they are approximately 0.056"


Not done any more tuning on the carb; I've had some overheating issues that were caused by a defective thermostat.


Thanks all, for the great advice in this thread!


Frederick

Hello Frederick,
I have been checking in on your thread and I did not see any activity, so I was wondering how your tuning has worked out. It is good to hear from you.

UPDATE:
I am waiting on my new jets and pvcr's to get here. After discussing this with QF, the stock pvcr's that came in my carb were .059". So they gave me a list of their next larger pvcr's and I chose the .065", .069", and the .071" to test. After looking at the area of my existing main jets and pvcr's, and knowing that I am currently lean, I am going to test the .065" pvcr's with the new .058 main jets. This combo will be richer than my current 060 main jets and .059" pvcr's when the pv is open. If this combo does not bring my light throttle 16+ readings down into the low 14's, then I will test the .069"' pvcr's and so on.
Plus I can retest my 3500(70mph)-4000rpm(apx 75-80mph) A/F to see if it comes up into the mid-high 14's with the 058 jets. If not, I also ordered 056 main jets too for testing if needed. Then I will have to retest my WOT A/F and adjust the secondary jetting again.

You don't need to use Pi or divide by 4 or any of that. Just add the sum of the squares and take the square root.

If you have 60 jets and 30 jets then that is 3600 + 900 = 4500. Sq root of 4500 is 67.

So a 67 jet is equal to a 60 main and a 30 PVCR.

If you know how to use Excel it is easy to make a little spreadsheet that adds the jets together. That way you can quickly see if a 58 main plus a 65 PVCR is richer or leaner than a 62 main with a 59 PVCR.

You're on the right track. If WOT is lean but the main circuit is fine, then keep opening up the PVCR until the AF is correct. Most people are too lazy to do it this way, but it is the only way to dial in a Holley type carb for both economy and performance.

Once you get this carb dialed in you'll be ready for a real challenge such as a three circuit Dominator!

"If WOT is lean but the main circuit is fine, then keep opening up the PVCR until the AF is correct."

Andy,
If the main circuit is fine, why not just go up on the secondaries to achieve the required WOT A/F?



Thanks allot,

Guess that depends on the throttle position during "normal" driving.

Mattax

Sorry about typing the ""3.1415 x main jet x pvcr = volume"" because I was in a hurry and I typed it wrong. The formula that I found was "3.1415 x jet x pvcr /4 = total area" but then I found that just multiplying the main jet and the pvcr gave me what I was looking for.

The only time that I am seeing the 16+ A/F is during medium accel "only" when the vacuum falls under my pv rating. So when the pv is open is when I was seeing this 16+ on the A/F meter. This is why I am changing to the richer pvcr's.

My main jetting is still a little rich at 14.4 and that is why I am dropping the main jet by 2 to see where the A/F falls. The mains were showing 14.0 then I dropped the main jet by 2 to give me the current 14.4. So now I am dropping the main jet again by 2 hoping to get me in the 14.6-14.8 range.
This is the same chart that I showed above. It appears that my mains are starting in around or after 60mph (referencing my past charts)
- 35mph=14.6
- 40mph=14.4
- 45mph=14.8
- 50mph=15.0
- 55mph=15.2
Above rpms can be changed with transition circuit tuning changes.

- 60mph=14.6 (3100rpms) [mains starting?]

Below rpms can be changed with main circuit tuning changes.

- 3500rpms=14.4(60 jets) [was 14.0 w/62 jets, was 13.8 w/64 jets]
- 4000rpms=14.4(60 jets) [was 14.0 w/62 jets, was 13.6 w/64 jets]
As you can see by the jetting progression, the 58 main jets should get me to where I want to be for the upcoming cooler air temps.

Thanks

Good morning!

Quote:

---

Sorry .. I was in a hurry and I typed it wrong... but then I found that just multiplying the main jet and the pvcr gave me what I was looking for.

---

No apology needed..this way you know who is paying attention (and admitidly I only check in sporadicly)
not sure about the multiplying, it's what AndyF wrote, its the areas that need to be compared. PI*r^2
but as Andy pointed out, its the square of the radius thats different.


Thanks for reposting the chart summary. That's really good.

Quote:

---

The only time that I am seeing the 16+ A/F is during medium accel "only" when the vacuum falls under my pv rating. So when the pv is open is when I was seeing this 16+ on the A/F meter. This is why I am changing to the richer pvcr's.

---

So my question is this whether the lean surge also occurs above the PV opening vacuum?

It's normal for the AFR to get leaner as the throttle opens. This is fine as long as load on the engine is not too high. Somewhere around 80-90% load (depending on the engine design) it needs to be richer. The vacuum where each engine-drivetrain combo hits the load that requires enrichment can vary quite a bit. Maybe you'll have to go to a 10.5 PV.

However when the PV does open, the AFR should not get suddenly leaner if the carb is already on the mains (even partialy). Check the AFR at 12" and 10". If its already around 16:1 or higher, then 16:1 at 9.5"vac at least makes sense. If AFR is richer at 10 and 12"Hg than at 9", then something is not right.* If its continuing to get leaner below the PV opening vacuum then the PV is probably not opening when it should be.

*one possible but unlikely scenario is that the fuel level is below PV

Hope that helps some.