Lean AFR for multiple seconds on high load (Brawler 670cfm vac)

Metalmarty

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Hi All,

I've created a new thread since I've bought a new carb, which is working a lot better already.
Previous thread can be found over here : Holley 750dp lean secondary tip in

I've replaced my carb with a Brawler 670 vacuum secondary BR67256 and I'm currently trying to jet the Brawler for optimal performance.
With some small changes it's already working a lot better than the 750DP I had.
Driving on low load is going perfectly well, nice AFRs. Good throttle response.
However, it's going very lean when giving it more than half throttle, and it stays lean for multiple seconds before getting back to normal AFR readings.

The brawler 670CFM vacuum is new, out of the box.
Floats are set on the car, halfway sight glasses.
Idle screw are only a half (0.5) turn opened up, more is way too rich
Primaries are set to show just a little bit of the transfer slot (square) and secondary opening has factory setting.
Vacuum pot screw it set to one full turn (1.0). (was 1.5 from factory)
Idles at 900rpm.
Primaries:
- IFR 32
- LSAB 70
- HSAB 28
- Main jet 72
- PV 8.5"
- PVCR 43
- Squirter .35
- White cam

Secondaries:
- IFR 32
- LSAB 70
- HSAB 28
- Main jet 77
- PV plugged

Some background information.
I've got a wideband AFR gauge, vacuum gauge and rpm gauge installed.
- Idle vacuum is around 18inhg
- Steady state cruise vacuum is around 21 inhg (steady state 30mph and steady state 50mph)

Idle AFR is around 14.
Steady state cruise AFR is around 14 at 30mph and 50mph.
If cruising at 30 or 50mph and giving it more than half (or WOT) throttle it goes very lean (16-18AFR) for multiple seconds (with noticeable hesitation).
After a couple of seconds it seems to catch up, starts to pull hard and goes down to 12.5-13.0 AFR, which is perfect.

Car information.
It's a 1968 Chrysler Newport 4dr HT, weighs 4600 LBS.
- mopar BB 400 ('77 smog era, around 7.5:1 real compression)
- Stock 452 heads
- Edelbrock dp4b intake (aluminium dual plane)
- Brawler BR67256
- Mopar performance style electronic ignition, 16 initial, 38 all in
- Stock .430/.434 cam
- hedman 78070 headers with 2x 2.5" full dual exhaust with magnaflow mufflers and AP resonators
- 2300 stall converter
- 3.23 gears

Does anyone have any tips for me what I can do to get rid of the lean spot? :)
I've got a box of main jets (64 upto 99)
If got a box of air bleeds on the way (.065 - .075)
I've got multiple power valves (5.5, 6.5, 8.5, 10.5) (I've tried 10.5" since I'm getting 21" at 30/50mph steady state), but that opens too early, making the lean spot at high load way worse)

I'm planning to up the LSAB from 70 to 73 to get a better response out of the idle mixture screws.
They are really touchy and opening them more than half a turn makes it pig rich.

Adjustable vacuum pot screw is screwed out 1 full turn (was 1.5 turn from factory). Should that be turned in even more?

What more should I do?
 
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USSMOPAR

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sounds over-jetted out of the box
a 195 thermostat is required
block the intake crossover
whats the underhood temp after a hot soak at the base of the carb?
same old tuning issues...it is 2022 not 1968-72
 
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Metalmarty

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sounds over-jetted out of the box
a 195 thermostat is required
block the intake crossover
whats the underhood temp after as hot soak at the base of the carb
same old tuning issues...it is 2022 not 1968-72

It was under jetted out of the box...

It had 70 primary main jets and 74 secondary main jets and was too lean on the AFR gauge with multiple different loads. I've spend multiple runs changing main jetting to 72 primary and 77 secondaries. Way better now on light and mid load and om WOT (after a couple of seconds being lean it pulls and goes to 12.5-13.0AFR)

I've got a 180F thermostat. And the water temperature stays dead solid on 180-185F when up to temperature and driving.

Intake crossover is blocked.

No specific underhood temps, but not too hot. I can still touch the carb when the engine is at operating temp and after driving in 80F weather.

"it is 2022 not 1968-72"
So? What does this have to do with my problem?

Any other ideas what can fix my lean problem at high load? I wanted to try to turn the vacuum adjustment screw a little more in (0.5 turn open instead of 1.0), slowing the opening of the secondaries, see if that improves the situation and fine tune from there. Maybe the secondaries are still opening too fast...
 

CBODY67

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Did the Brawler come with a single-stage or two-stage power valve? Which CAN relate to the main jet sizing.

On the two-stage valve, usually they start to open at 10.0" Hg, with full open by 5" Hg. On the emission-spec 4160 I had on one of my cars, which was a new carb, it was easy to see when the power valve openned, with the car in gear and the parking brake fully applied, and then slowly openning the throttle (with the accel pedal) to lower the engine vacuum. In gear, with the a/c running, it would pull 10.5" Hg. The two-stage power valve which came in the carb was rated at 10" Hg. Adding just enough throttle to decrease the intake manifold vacuum would result in a slight richening of the mixture, BUT when the manifold vac dropped to 5.5" Hg, a BIG increase in richness happened.

Per the "70" main jets, might be a slight bit toward lean, but the "72" sound like they should be "ballpark", as I recall. But then, I recall a LOT of the middle-1960s Holley 4160s which had "65s" in them from the factory, pre-emissions.

When emissions started to get a bit more stringent, Holley leaned the main jets one or two notches and THEN used the two-stage power valve to help cover it a bit. Jets a bit leaner for steady-state cruise (and fewer on-road emissions), but a bit more enrichment under slight load increases, but not needing full enrichment. So the two-stage power valve was devised to cover that possible part-throttle lean condition, under certain driving situations.

The Holley website has a full listing of power valves, single and dual stage, with various flow rates. Which can get a bit confusing, at times!

To vary the timing and rate of opening of the secondaries, THAT happens with the various secondary diaphram springs. You can buy a Spring Kit from Holley direct or via places like Summit Racing. OR possibly some speed shops might have them in stock. Due to the nature of the Holley vacuum secondaries, the secondaries should NOT open without any load on the engine, according to Holley. SO . . . an open element air cleaner can help you hear when they open, from my experiences. By design, they will only open as needed, so getting them to open quicker usually takes a weaker spring than the carbs are shipped with.

By nature, ANY of Holley's non-OEM-spec carbs are "will-work" in orientation, although they usually advertise them for specific CID ranges. With the 350 Chevy applicatins firmly in their cross-hairs. I'll admit that I have not kept up with all of their marketing names and what the differences might be between those newer carbs, which is why I usually lean toward the OEM-spec carbs when possible (although not very possible in later years). Although Holley is "famous" for taking one OEM carb numbrer and "universalizing" it in later versions. The 1971 Super Bee 383 Holley is one example . . . now it comes with race bowls, electric choke, and a few other tweaks. Similar with the 0-9895 QJet replacement (for a '79 L82 Corvette), sans the race bowls. BTAIM

At what point in the exhaust flow is your oxygen sensor located? Just curious, as when I had my car hooked up to a Sunn emissions test/tune-up diagnostic machine, with the sensor at the end of the exhaust pipe, they usually recommend to wait 30 seconds or so from each idle mixture adjustment to take readings. Takes that long for the changed mixture to get to the back.

In the mean time, I'll peruse the Brawler line to see what features they might have. To see if there's something there I might not be aware of.

From my experiences and observations,
CBODY67
 

USSMOPAR

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2022 Today's fuel requires 195 degree min operating temp to atomize well.
It tends to collect inside the intake and burn off in the cruise mode ping ponging the af. The cars actually run better at 195 than 180. I have been tuning hot rods for years with good instrumentation and more, my cars pull away from every one else. Be aware of hot underhood temps but the temp gage shows ok
 

Knebel

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OK few questions. Does this happen when you open the throttle fast or just slow to keep up with load?

I would put a 6.5 Power valve in and test that first. If no change, lighter spring for the vac secondaries.
 

1970FuryConv

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At what point in the exhaust flow is your oxygen sensor located? Just curious, as when I had my car hooked up to a Sunn emissions test/tune-up diagnostic machine, with the sensor at the end of the exhaust pipe, they usually recommend to wait 30 seconds or so from each idle mixture adjustment to take readings. Takes that long for the changed mixture to get to the back.
Oxygen sensor location. Good question!
 

Metalmarty

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Did the Brawler come with a single-stage or two-stage power valve? Which CAN relate to the main jet sizing.

On the two-stage valve, usually they start to open at 10.0" Hg, with full open by 5" Hg. On the emission-spec 4160 I had on one of my cars, which was a new carb, it was easy to see when the power valve openned, with the car in gear and the parking brake fully applied, and then slowly openning the throttle (with the accel pedal) to lower the engine vacuum. In gear, with the a/c running, it would pull 10.5" Hg. The two-stage power valve which came in the carb was rated at 10" Hg. Adding just enough throttle to decrease the intake manifold vacuum would result in a slight richening of the mixture, BUT when the manifold vac dropped to 5.5" Hg, a BIG increase in richness happened.

Per the "70" main jets, might be a slight bit toward lean, but the "72" sound like they should be "ballpark", as I recall. But then, I recall a LOT of the middle-1960s Holley 4160s which had "65s" in them from the factory, pre-emissions.

When emissions started to get a bit more stringent, Holley leaned the main jets one or two notches and THEN used the two-stage power valve to help cover it a bit. Jets a bit leaner for steady-state cruise (and fewer on-road emissions), but a bit more enrichment under slight load increases, but not needing full enrichment. So the two-stage power valve was devised to cover that possible part-throttle lean condition, under certain driving situations.

The Holley website has a full listing of power valves, single and dual stage, with various flow rates. Which can get a bit confusing, at times!

To vary the timing and rate of opening of the secondaries, THAT happens with the various secondary diaphram springs. You can buy a Spring Kit from Holley direct or via places like Summit Racing. OR possibly some speed shops might have them in stock. Due to the nature of the Holley vacuum secondaries, the secondaries should NOT open without any load on the engine, according to Holley. SO . . . an open element air cleaner can help you hear when they open, from my experiences. By design, they will only open as needed, so getting them to open quicker usually takes a weaker spring than the carbs are shipped with.

By nature, ANY of Holley's non-OEM-spec carbs are "will-work" in orientation, although they usually advertise them for specific CID ranges. With the 350 Chevy applicatins firmly in their cross-hairs. I'll admit that I have not kept up with all of their marketing names and what the differences might be between those newer carbs, which is why I usually lean toward the OEM-spec carbs when possible (although not very possible in later years). Although Holley is "famous" for taking one OEM carb numbrer and "universalizing" it in later versions. The 1971 Super Bee 383 Holley is one example . . . now it comes with race bowls, electric choke, and a few other tweaks. Similar with the 0-9895 QJet replacement (for a '79 L82 Corvette), sans the race bowls. BTAIM

At what point in the exhaust flow is your oxygen sensor located? Just curious, as when I had my car hooked up to a Sunn emissions test/tune-up diagnostic machine, with the sensor at the end of the exhaust pipe, they usually recommend to wait 30 seconds or so from each idle mixture adjustment to take readings. Takes that long for the changed mixture to get to the back.

In the mean time, I'll peruse the Brawler line to see what features they might have. To see if there's something there I might not be aware of.

From my experiences and observations,
CBODY67

This Brawler has a single stage power valve. Secondary metering block is plugged and not drilled for PV jets.

It currently has an 8.5" PV. I've tried a 10.5 first, since I have 21" cruise vacuum, but that didn't work well. I went down to a 8.5 (18" Idle vacuum divided by 2) and that worked way better. The power valve has 0.043" jets.

The brawler has a purple spring in the vacuum secondaries. It has a screw adjustable opening point and rate, just like the QFT carbs. It's 1.5 turned open from factory. I closed it to 1.0 turn open. I might have to bring it down even more to prevent the lean situation. We have more springs in stock, but according to brawler it shouldn't be needed since it has this adjustment possibility.

022-brawler-carburetor-holley-vacuum-air-secondary-adjustment-mopar-273.jpg


This brawler is also aimed at a 350cid chevy. That also explains why it was a tad lean out of the box :)

The Lsu4.9 Oxygen sensor is installed in the top of the 2.5" tube. It's located about 10inch from the collector and about 2.5ft from the exhaust port in total. This is also what it advised from bosch and multiple tuners for optimal response.

O2 sensors in the back of the exhaust are really slow indeed.

2022 Today's fuel requires 195 degree min operating temp to atomize well.
It tends to collect inside the intake and burn off in the cruise mode ping ponging the af. The cars actually run better at 195 than 180. I have been tuning hot rods for years with good instrumentation and more, my cars pull away from every one else. Be aware of hot underhood temps but the temp gage shows ok

I will keep this in mind. Thanks :)
I'm always keeping an eye open for engine and under hood temperature. I've placed gauges for oil pressure, water temperature, rpm, voltage, AFR.

OK few questions. Does this happen when you open the throttle fast or just slow to keep up with load?

I would put a 6.5 Power valve in and test that first. If no change, lighter spring for the vac secondaries.

It's the worst when I open throttle fast. The lean condition is less when I open the throttle with a lot of ease. The slower the better. This also makes me suspect the vacuum secondary opening rate even more. Might have to slow this. I wanted to test that today but something came up... Hopefully tomorrow.

Oxygen sensor location. Good question!

Good question indeed.

The Lsu4.9 Oxygen sensor is installed in the top of the 2.5" tube. It's located about 10inch from the collector and about 2.5ft from the exhaust port in total. This is also what it advised from bosch and multiple tuners for optimal response
 

Knebel

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I would play with the rate of the secondaries first. If that does nothing then i would look at the accel pump nozzle and cam.
 
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