I don't have all my numbers with me on my carb right now because I'm at work but I do know that I called Quick fuel about my rich problem at idle and they had me up the size of my air bleeds at each corner. I have noticed that this carb is very touchy when it comes to setting the four corner idle ajustments. When I adjust it with the vacuum gauge it ends up a bit rich when done aroud 13. So I just screw those in until I get it close to read 14.1 or so. It's been way to hot this summer so I haven't done alot of messing with the car. I noticed last week when I drove it to a car show that was about 20 miles one way that the cruise reading was right at 13.8 to 13.9 and I know I could jet down to bring that reading a little closer to 14. The plugs have been showing good color with these readings so far.
When I rebuilt the motor I just ran it with that carb right out of the box and it was so rich that it washed out the rings or what ever it did. I had a issue come up over winter when I changed out my stock heads to run edlebrock performer aluminum heads. The pistons where slapping against the bottom of the heads so, I had to tear the motor apart again and thats when the engine builder found the problem with the rings. Thats when I decided to buy the air fuel gauge and learn how to dial in the carburator. Like I said before I've enjoyed reading your post and it has helped me alot on setting up my carb.Thanks again
Pat Faley

"" I noticed last week when I drove it to a car show that was about 20 miles one way that the cruise reading was right at 13.8 to 13.9 and I know I could jet down to bring that reading a little closer to 14.""

If you need to "tweak" the cruising A/F ratio, you could change your IAB's or raise/lower your front float. This might be easier than swapping the jets, especially if you are only looking to change the A/F by less than .4 or so. If you do either one of these, then remember to reset your idle A/F mixture again.


""I have noticed that this carb is very touchy when it comes to setting the four corner idle ajustments. When I adjust it with the vacuum gauge it ends up a bit rich when done aroud 13. So I just screw those in until I get it close to read 14.1 or so.""

I found the same results. 13.0 at idle can really smell up the garage in a hurry and 14.0 really cleans it up. My metering screws are very sensitive too. It only takes a fraction of a turn from any one of them to see the results on the meters.

Thanks for the reply.

I am continuing my testing on stagger jetting for WOT. As previously mentioned, I was able to stagger jet my secondaries to give me a .2 difference in my WOT readings from the drivers side to the passenger side. But this Summer, I am now back to seeing a .4 difference side to side at WOT.
Since my drivers side is the lean side at WOT, I decided to keep my jetting the same (I am just trying external adjustments to see if I can correct this) and try testing with different HSAB's on the drivers-secondary corner only. I was running with .039" HSAB's (all around) and found the .4 difference. Then I dropped down to a .036" (drivers-secondary only) and the difference became .2 again side to side. So I tried to go down again to a .033" which I thought would be perfect, but the .2 spread stayed the same. I do not have any .030/.031" to test with, so I was thinking of dropping both the front and the rear drivers HSAB's to the .036's to see what happens, but I am 99% sure that will change my cruising A/F which is already dead on.
I am also thinking of dropping both of the secondary HSAB's down to .036 or to .033 to see if the passenger side will help richen the drivers side. I am ok if the passenger side richens up just a hair, but I am mainly concerned with dropping the A/F of the drivers side.

Review:
I would like to alter the drivers side A/F by .4 at WOT.
I want to keep my primary side the same since my cruise A/F (and all the way up to 4000rpms) is right at the 14-14.2 which is my current goal.
I have a feeling that I may be opening up the carb and adding another 2 jet sized to the drivers secondary though.

Any additional thoughts?

Thanks

EDIT:
I have decided to stay with my .039" HSAB's (all around) and go up on my secondary jetting. I need to richen my drivers side by .4 and my passenger side by .2 (it is close!). So I decided to go up two jet sizes on both secondaries (the stagger in the rear is still 6 jet sizes) and retest.

Y07_A66:

Have you ever watched your AFR while power braking? I have a very tight convertor behind my motor, and my motor will go dead lean (17.x) when trying to bring the RPMs up against the converter. If I bring up the IFRs (.035) I can reduce the affect and at some RPM point the mains start and the AFR drops back down. My cruise is ugly rich, so I don't want to raise the IFRs, and am also reluctant to drop the HSABs (current .035). In general my QFT carb is possessed, and is off the motor again, but I am wondering if you have any experience under these sort of conditions, particularly with the large HSABs in place.

Thanks for continuing to update your thread!

Dave,
I have not watched the AFR while power braking to witness a lean condition. The only lean condition that I have right now is when I am cruising and I very slowly get into the throttle for a few seconds (before the seconds kick in). Then I see the AF going into the high 15's during this situation. I was lean into the 16's until I raised my front jets up by two and then it richened up slightley. I am going to see if the .033" IFR's helped with this issue. If not, then I will bring up the main jets by another 2 sizes.
My A/F gets rich quick when I drop down the HSAB's. The .039's work great on mine. My cruising A/F is always in the 13.8-14.4 range with .062 main jets, .060" IAB's, and I just recently changed the IFR's from .031 to .033's. My WOT numbers are in the high 12's and I am working on bringing that down to the 12.5-.6 range.

""My cruise is ugly rich, so I don't want to raise the IFRs, and am also reluctant to drop the HSABs (current .035).""

I have been tweaking my cruise A/F with my IAB's and my front float level. Since my HSAB's are leaner with the .039's, and my main jets are leaner with the 62's, I am using .060" IAB's to keep my cruise A/F as mentioned above. I also had to go richer on my PVCR's to .071 to help out on the acceleration.
If you go with the .035/.033" HSAB's, can you lean out your cruise with leaner IAB's?

"My A/F gets rich quick when I drop down the HSAB's. The .039's work great on mine."

My biggest HSAB is .035, and I hadn't considered trying to go bigger because it seems I already have an issue with the mains not flowing enough soon enough, with an increasing load on the motor. As mentioned, it is hard to bring up the RPM against the converter without causing a nasty lean miss. Vacuum is a around 10" and there is no way for the transition circuit to deliver enough fuel, at least up to a .035 IFR. Perhaps I should try bigger HSAB but it just seems that I am moving the problem around and I don't know a good way to cover the hole between the transition and mains.

If I had a looser converter, then I know the load would be less at lower airflow (which would help), and I may have to change the converter sooner than I wanted. I have been hoping to get the motor running decent, and then get it on a chassis dyno to get some numbers to better judge future converter characteristics. In general, I just don't like a loose converter on a primarily street driven car. I'm an old 4-speed guy, and I still miss the fun of throttle responsiveness under small "gooses" when going thru the gears, and I have been hoping the tighter converter would help with the fun factor.

"If you go with the .035/.033" HSAB's, can you lean out your cruise with leaner IAB's?"

I have tried as high as .075 IAB, and it helps the cruise some (getting into low, low 13s) but it causes a problem with the low end of the transition circuit (too lean) while putt-putting thru the neighborhood.

Over the past two years I have been all over the map with carb settings. I've found various other issues as well, but still cannot obtain a setup where all of the carb circuits work well at the same time. My motor seems to be possessed at times!

Are you using a High Flow PV?
Have you tried increasing the IFR's (beyond .035") all around? You may not be able to cruise on the transition circuit very long with your setup.
I would not go leaner on the HSAB's in your situation. You are correct, this would just delay the mains.
What is smallest HSAB that you have tried?
My "guess" would be to go smaller on the HSAB's and larger on the IFR's to richen up the transition circuit to main circuit lean spot.

How much testing have you done with the front jets? It is hard to pin point when the mains start (even while watching and charting off of an A/F meter), but have you tried going up on your main jets with the smaller HSAB's to see if this helps down low in the rpm range?


Would you mind reminding me which QF carb you have?

Thanks allot for your replies.

Y07_A66:

My carb is the QFT-850-PV. It is advertised as a race carb but has vacuum secondary, and I am using for a street(mostly)/strip vehicle. The carb is on my 400/470, with E-Heads, RPM Manifold, and a 248@.050 solid flat tappet cam. The 727 has a stock 440 converter in it at the moment, and the rear has 3.55s. The converter needs to change at some point, but as I said I was hoping to get a solid tune before deciding exactly what to get. My car is a 70 Barracuda, and given its weight, the CI of the motor, dual plane, and a vacuum secondary carb, I felt I could get the combo going decent.

I know most folks first response is that I should be using a big DP and lots of stall in the converter. However, I am just not convinced that is right for me. When I first put the car together I had a MP 175K converter in it, and it was like slush. I know folks rave about the more modern converters. The thing I miss is the ability to goose the throttle and get the instant response like with a 4-speed. When I had the MP 175K in it, I would goose the throttle and all that would happen is the RPM would jump and the exhaust note would rise. You had to push deeper into the throttle to get past the flash point before it would get fun. For example at highway speed, the motor turns around 3K. I could use the throttle and move the RPM from 3-almost 4K with little change in instantaneous speed. The thing was too loose for my taste, at least given the torque of the motor.


--Are you using a High Flow PV?

Yes, I use the ones from QF. Currently it has a 7.5" one in it. Original one was a 4.5".

--Have you tried increasing the IFR's (beyond .035") all around? You may not be able to cruise on the transition circuit very long with your setup.

The original IFR when new was .036. I have not tried above that. I have tried as low as .031 but the off idle problems were fairly bad. If I move the IFR down, I can at least get the low speed (say 30-40MPH) AFR somewhere reasonable. At times I have had this in the mid-14s. Out of the box, the low speed AFR was in the high 11 to low 12 range.

--I would not go leaner on the HSAB's in your situation. You are correct, this would just delay the mains.

Factory was .033 HSAB.

--What is smallest HSAB that you have tried?

I have not tried smaller than .035 with my power brake test. This behavior was something I recently discovered. However, it possibly explains why I felt I could not go below 72 primary jets (factory was 76) because of the lean miss when I tipped into the throttle. My smallest HSAB is .025. During the past 2 years, I have had as small as .030 HSAB in there but I would have to review my records to see what pri jet was in at that time.

--My "guess" would be to go smaller on the HSAB's and larger on the IFR's to richen up the transition circuit to main circuit lean spot.

Good thought, although I would likely start going back down in the HSABs before coming up further on the IFR, just because of AFR in the 1500-2000 range.

--How much testing have you done with the front jets? It is hard to pin point when the mains start (even while watching and charting off of an A/F meter), but have you tried going up on your main jets with the smaller HSAB's to see if this helps down low in the rpm range?

I'm sure that might help in the low RPM range, but at cruise that would be a real killer. At times, I worry about washing out the rings. I have had AFR as low as in the 10s under light throttle. The funny thing is that the motor wants LOTS of fuel at WOT. At one time I removed the PCVR and run 72 pri, and the AFR was 12.2 at WOT. With .061 PCVR and 74 jets, the WOT AFR is in the low 14s (secondaries disabled).

I still believe there is something wrong with the carb. Besides being pig rich, the AFR will have wild swings (to the rich side) during highway cruise. This does not occur in the 1500-2000 range. The motor is getting extra fuel from somewhere but I can't find it. I have spoken to QF a few times on it, and tried everything they suggested to no avail. I know this problem is carb related because my 30 year old 3310 does not do it. The 3310 is on the motor right now, but of course it is not so adjustable and it has its own AFR problems.

With respect to seeing the mains start, the power brake test is a very easy way for me to learn this, at least given the current gap between transition. I keep a vacuum gauge in the car, and you can see it go down as the RPM goes up (standing on the brakes) with the AFR going up, until the mains start and the AFR drops back down. If I get adventurous I might put the QF back on the motor, and shoot a video of it!

Sorry for the length, and thanks for your thoughts. I have a friend in the neighborhood, and he keeps trying to talk me into FI. After all the time and frustration, he is starting to sway me! I don't know if JimG is still around, but we use to discuss the difficulties of getting a good highway tune on a street driven BB, and I don't think he ever got to a satisfying point in his efforts either.

with wild swings of aft at cruise is to possible fuel is puddling in the manifold and then being evaporated into the mixture every now and again? ultimately i would believe that the air fuel charge is falling out of suspension in a dual plane or maybe there is some reversion going on in the intake, valve not sealling all the way, etc? there is a reason port efi is the way to go to minimize variances like this.

i do however applaud your stick-to-itiveness on getting the carb working. i will be following suit shortly and am eagerly following your progress.

--with wild swings of aft at cruise is to possible fuel is puddling in the manifold and then being evaporated into the mixture every now and again? ultimately i would believe that the air fuel charge is falling out of suspension in a dual plane or maybe there is some reversion going on in the intake, valve not sealling all the way, etc? there is a reason port efi is the way to go to minimize variances like this.

Jerry, this is an excellent thought and one I had not considered before! The AFR at cruise is certainly very rich. The motor turns 3K at 65, and I'm not sure if fuel would drop out at that point or not. Have you seen this before?

I don't see the same effect with the AFR swing with my 3310 but it may just be that it is not quite as rich as the QFT carb at cruise.

There is also definitely reversion as well, and I often see small amounts of raw fuel if I pull a vacuum cap off one of the vacuum fittings on the throttle plate. My cam is in at 109, and I have been toying with the idea of advancing it some over the winter. That would reduce the reversion some.

I don't think it is a valve sealing issue since I have adjusted the valves many times, and have run both compression and leakdown tests, and don't see anything odd.

EFI certainly has big advantages, but it does come at quite a cost, at least to support the type of HP levels the motor should be capable of.

i personally have not witnessed it but it doens't have to have any outward signs either. i don't know what kind of dual plan your running but dual planes have the really long runners with narrow ports usually that have alot of curves. it doens't take much for fuel to fall out of suspension and create a wet wall. are you running your heat crossover or is it blocked off? really you won;t be able to identify fuel puddling runner issues unless you sample egts at each cylinder. your o2 sensor won't tell you enough.

advancing the timing and running a cam with less overlap will help with the reversion as well.

I run the Edelbrock RPM intake; it doesn't have a heat cross over. It was into the 90s yesterday though. The motor is a low deck big block, currently at 470CI. I am really warming up to the idea of some sort of fuel pooling, and I appreciate the thought. The AFR swings don't occur at low RPM, nor at WOT regardless of RPM. It only seems to occur at a certain RPM range. Advancing the cam timing looks to be in my future; hopefully that will help.

Yesterday I tinkered some with the carb using a thought from Y07_A66. I dropped the main jet down significantly (to 69s). To my surprise, this really leaned out the low RPM range, even causing a lean miss from off idle and up. I switched in my biggest IFR (.036) and it was still lean. Then I dropped the IAB from .070 to .065 (the smallest I have), and it improved some to the point where the car was just driveable, but still way too lean (16-17 AFR). Never had this problem before! So, now I am going to need to buy some bigger IFRs. I didn't want to drive it much, given the AFR, and didn't get a chance to take it far enough to try highway speed.

Dave,
Please keep us posted and thanks for sharing.

Ref: From what I have found so far, swapping all four IFR's from one stock size to the next will net the largest cruise AF change, around .6-1.0. Swapping all four IAB's from one stock size to the next will net around .4-.6.

Y07_A66:

I plan on buying each larger IFR from 037 to 040. That should cover me. I'm only planning on swapping the primary IFR since the goal is to improve the off-idle and low RPM mixture. Did you ever try just changing the primary IFR? To me, it seems the secondary IFR really shouldn't be delivering incremental fuel in the 1K-2K RPM range but I could be wrong.

Hope to have more results next weekend.

Yes. I ran .033 IFR's in the front for several weeks with .031's in the rear. It was just for testing purposes, so the next time I pulled the rear metering block I added the .033's to the rear just to keep them even so I did not forget what setup I had.
My theory was I only needed a small change, so I only did it on the primary side. I have been told to keep them the same front to back, but it did help me at the time. When I had the .033's in the front, I did only adjust the front metering screws to make up the difference in idle tuning. I did have to lean the fronts after adding the larger IFR's, which makes sense.
I would suggest buying enough to do both front and back, then add them to the front to see if it gets you where you need to be. If you still need more, then add them to the back and retest.

Note: I do like to see my metering screws set the same front to back (same side) and I can do so with the same IFR's front to back. Since I added my second O2 sensor, my side to side metering screw settings are a little different but they are the same setting per side.

"" it seems the secondary IFR really shouldn't be delivering incremental fuel in the 1K-2K RPM range but I could be wrong.""

I still struggle with,,, why are there IAB's on the "secondary" metering block?
They still affect the idle circuit, so I am guessing that the IFR's on the secondary side are still affecting the idle circuit the same way as the primary IFR's are too.

"I would suggest buying enough to do both front and back, then add them to the front to see if it gets you where you need to be...."

Good approach. The QFT IFR jet packs come with a set of 4 so I will be good there.

"why are there IAB's on the "secondary" metering block?
They still affect the idle circuit, so I am guessing that the IFR's on the secondary side are still affecting the idle circuit the same way as the primary IFR's are too."

Yes, I agree the function is exactly the same as on the primary side. On a mechanical secondary carb, it is feasible that the throttle is open just far enough to crack the secondaries. On a vacuum secondary carb, I am doubtful that such a state could be obtained but even there it may be possible. Even when in such a state though I don't think the secondaries would operate on the transition circuit since the airflow demand of the motor should quickly start the mains. I'm not certain about this, so the advice to keep the IFR square is reasonable. For now though, I don't want to have to keep pulling both fuel bowls.

I was working on my stagger tuning to get both sides to show 12.5-12.6 from 50mph cruise to WOT. As I may have noted earlier, my drivers side was leaner than my passenger side by .4. So in order to change this, I stagger jetted my secondary jetting. I started at 74 per side and found the drivers side to be lean. So I tested 76(D) and 74 (P) and it helped a little. Then I tried 78/74 and it stayed the same which did not make sense. Then I tried 80/74 and it stayed the same and then I tried 82/74 and both sides still read the same.
Now I am thinking that something is not right. This much stagger jetting towards the drivers side secondary should have made the car run RICH at WOT, but it did not. Then on my next drive I noticed that my cruise was going lean on both sides, my idle was going lean on both sides, and when I slowed down to a stop the car would want to shut off and was leaning out into the 15's in D at a stop. I just reset my idle in D to 13.8/14.0 but then when I came to a stop it would lean out again to the 15's.
I found out that my fuel pump was going out on me and I put in a new one and now my A/F numbers are back on track.
One of my previous issues (besides the 50-WOT readings beeing different) was when I was at a steady cruise and I would slowly push down on the throttle, the sensors would lean out into the 15's. I had this about a month ago and it was leaning into the 16's during the same situation so at that time I raised my main jets from 60's to 62's and this issue started showing the 15's. I rejetted the mains again and now I am running 64's up front and with my new fuel pump, I am no longer seeing the cruise to light accel dropping into the 15's. I am showing mid 13's at cruise (will be leaning this out to low 14's) and my light throttle stayed right around 14-14.2 before the seconds kicked in. This was good!
Now I am going to lean out my IAB's from .060's to 064's to get my cruise (40mph-70mph) back into the 14.0-14.2 range.
My secondary jetting: now that I have the new fuel pump and 064 main jets, I will swap out the secondary 78/78 for 76 (D) and 74 (P). This should get both sides right around the 12.5-12.6 number.
So my secondary stagger issues were getting worse because my fuel pump was not keeping up with the larger jetting on the drivers side. Now that I have the new pump, my 78's are too rich (12.4 (D) and 12.0 (P)) and I will rejet and retest.
UPDATE:
76 (D) and 74 (P) gave me a 12.8 (D) and a 13.0 (P) side 50-WOT. So I am now within .2 again from one side to the other. I am going to raise the rear float and see if I can bring the WOT number down about .2-.4 on both sides.
The IAB swap now give me a 13.4-14.0 cruise A/F. I just noticed that my mains appear to start in right around 55mph. My 50mph showed 14.0/14.2 and my 60mph showed 13.4. I might have to try something to lean this out again.

Y07_A66:

How did you isolate your fuel pump problem? Flow test?

I also had a chance to tinker today. I went from .036 to .037 IFR, which helped improve the low speed behavior. However, I discovered that some instances of my lean miss (AFR>17) are when pressing a little on the throttle. Vaccum is dropping to the 12-10" range, and I suspect the main are starting to flow at this point. My conclusion is that the 69 pri jets are way too lean, and I don't think further increasing the IFR is going to help under this condition. The motor was running well enough that I decided to take a quick highway run, and to add insult a WOT from 60MPH started with AFR in the 12's but then I watched as it dropped into the 11's then into the high 10's! This was from about 3K to 4.2K in high gear. Obviously my HSABs are also too small. So I have to go back up in size on both the pri jet and the HSAB.

I am not sure that I actually isolated my lean problem before I fixed it. I first thought that I might have had a vacuum line come off but after checking them, they were either new or had tight connections. I did hear a ticking noise coming from the pump area, so after going thru my notes and seeing what the A/F outcome was after changing my drivers-secondary jet (farthest jet from the fuel pump) from 74,76,78,80, then 82 with no change, and after all of the weird lean issues during my previous drive, I took a stab at replacing the fuel pump.

""I discovered that some instances of my lean miss (AFR>17) are when pressing a little on the throttle. Vaccum is dropping to the 12-10" range""
- Main jet sure sounds correct to me too. You are currently using a 7.5pv, what about using a higher rated unit? Your mains might just be starting which means your pv might help being higher once the mains are full on.

""a WOT from 60MPH started with AFR in the 12's but then I watched as it dropped into the 11's then into the high 10's!"
- The first dip into the 12's sounds good. What about the rear jetting? Could it be too rich? If you go up on the primary jetting, this issue will get even richer. What about a 4-6 jet drop on the secondary side? The HSAB swap would be a quicker test though.

Note: I just make a 4 jet swap on the passenger secondary side and a 2 jet swap on the drivers secondary side and it netted me 12.0 to 13.0 on the passenger side and a 12.4 to 13.0 on the drivers side for reference. One full point with four jet sizes and about half of that with 2 jet sizes.

"You are currently using a 7.5pv, what about using a higher rated unit? Your mains might just be starting which means your pv might help being higher once the mains are full on."

7.5pv is about as high as I can go right now. My in-drive idle vacuum bounces in the 8-9" range. As I mentioned, the torque converter is really tight, which puts quite a load on the motor. I know a looser converter would result in higher vacuum, but I'm not there at the moment.

"What about the rear jetting? Could it be too rich? If you go up on the primary jetting, this issue will get even richer. What about a 4-6 jet drop on the secondary side? The HSAB swap would be a quicker test though."

Currently I am testing with the secondaries disabled. On my carb, I can just turn a screw to adjust the secondaries, and closing it down should stop the vacuum signal to the pod, disabling them.

Between the two issues, I am thinking I need to try going up in pri jets from 69 to 71, and perhaps bump the HSAB from .025 to .027 and try again. Factory HSAB is .033.