Thrust issues with AFR gauge and Brawler carb

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Dusterguy

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Few years ago I bought new Brawler 750 double pumper carb BR-67213. I was driving happily until this summer I got a wideband AFR gauge. I was supprised that according to the gauge it was running very rich at wot. Something around 10 afr. Stock jetting was 76 front and 80 back. I gradually decreased main jets size in front and back. Now im at 66 main jets in primary and 70 at secondary. Afr gauge still showing it is running rich at WOT. 11.6 afr. To me it sounds crazy that stock jetting could be so far off, could there be something else going on? Maybe the afr gauge isnt working properly? Has anyone experience about this carb in question?

Here is what my plugs looks like currently.
plugs.jpg



Carb

br67207_v1.jpg
 
I’m not sure,,,those plugs look really good to me .
Do you run this engine much at WOT,,,,,probably not ?

It’s hard to think you changed the jets 10 numbers,,,,and that was all it changed .
Good luck.

You were happy before the gauge,,,,,try to stay happy .

Tommy
 
I’m in a Love/Hate relationship with my AFR gauge! So I pretty much agree with Tommy, if you are happy with how it runs and drives, then maybe just be happy! If it’s not pinging, smoking, bogging, stumbling or stinking…then be happy. As for the plugs, if those plugs have been in the car a spell, then they don’t look too terribly bad to me. If those are after a few miles, then maybe it’s time to take a closer look. Otherwise be happy.
Just my $.02
 
Just read an article about using an AFR gauge and a vacuum gauge.
 
AFR in my opinion is a tuning “aide”, it’ll have you chasing numbers til you don’t know which way to go. That carb has a choke, it’s not somehow pulling closed is it? On that note have you made sure no air bleeds or passages are blocked in the carb? That it’s good and clean inside. There have been reports of machining chips being found in the past inside other Holley carbs. Beyond that the only other thought would be the power enrichment circuit, maybe the power valve channel restrictors are way too large. These are just some thoughts on my part.
 
Ok, for all the love the Brawler gets around here, these carbs at BEST come with every conceivable tune up in them you can think of.

I’ve seen them with all 4 emulsion holes open.

I’ve checked one with only one emulsion hole open.

I’ve seen different sized bleeds in the same carb.

Here’s a classic. I had a guy contact me a year or so ago. Brand new carb. He was having issues getting the engine rich enough which is usually not the problem.

After several phone calls and a long time on the phone, we figured it out. When the carb was built, the primary metering block came with the power valve channel restricters that had BLANK jets in it. The had no holes so when the power valve opened there was no extra fuel added.

That would explain why he was running some HUGE jets. Just piss poor quality control.

I’m not impressed with the QC, but it is now a Holley product so that to be expected.

Saying that, your tune up has issues. We have no idea what your timing curve is.

I’m all for guys buying an O2 sensor but before buying that tool, if you can’t at least half assed read a plug do not buy one. It will lie to you and the plugs won’t.

Looking at your plugs you are FAT. Everywhere. You are fat at idle and even though I can’t see down in the plug it’s pig rich in the middle too. And WOT like the meter says.

Before guys start buying O2 sensors they should be buying a pin gauge set, drill bits and taps. That way you can measure and correct junk like this.

Before you can get help, we need some information. Otherwise we will just be talking out our hats.

We need to know how much T slot is exposed. We need to know the sizes of the air bleeds. We need to know how many emulsion holes are open and how big they are. We need to know how big and WHERE the idle feed restricters are.

Do you run a PCV valve? You should be.

We also need to know your timing curve.

This is sad because at least back in the day you almost never saw a Holley with miss matched bleeds and junk like that. Holley should have gotten out of the carb market long ago. We’d all be better off if Holley went broke and moved on to that good night.
 
Aren't engines supposed to be rich at WOT? lol
 
Here are a few thoughts and suggestions that may or may not help. I'm assuming the o2 reads normal except at wide open throttle.

1. Try another carb and see if you get the same results.
2. Move the sensor to the other side of the motor to see if it reads the same.

Fuel distribution is not always the same for each cylinder in an engine. This is especially true with dual plane manifolds. Also not all cylinders respond the same to a jet change.

On my dyno I have an o2 sensor for each bank.
Remember that the o2 reading is an average of the 4 cylinders on that bank of the engine. One or more cylinders could be rich, lean or any combination. The same is true when looking at each bank of cylinders. One side can be rich and the other lean. Looking at sparkplugs helps but can also mislead you. Same with egts.

If it has headers, placing the o2 sensor too close to the collector can cause the sensor to be biased to a particular cylinder.

3. Try as as an experiment a main air bleed change.

I have found that sometimes when a motor doesn't respond to a jet changes that changing the main air bleed will move the air fuel ratio.
 
Where did you install the O2 sensors, for accuracy they need to be as close to the outgoing exhaust as possible.

Edit
Just read the optimal position for the sensor is 6 inches max from beginning of the collector
 
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In my limited experience, O2 sensors are as good as useless with a closed throttle and a cam with a generous overlap.
What I mean is this; the O2 may or may not be telling the truth, but what are you gonna do about it? You the tuner still need to chose a path, and there are too many paths available from that at-idle O2 reading.

>There is just way too much going on in the intake, and
> there are just too many more ways to screw it up with the Transfer-slot to Mixture screw alignment, that all too often
> accompanies excessive Idle Timing.
> at idle, even early combustion, with a big cam, is still gonna send unburned fuel and/or still burning fuel, into the header.That's part of why it stinks so bad. Your Power stroke may not be rich at all! maybe, only your exhaust is. You gotta learn to understand the difference, and the O2 cannot help you, cuz it's not in the cylinder! It only knows one thing, which you gotta interpret.
And on the overlap stroke, your header can yank fuel charge straight from the plenum right across the TDC-dwelling piston and into the header it goes; unburned. What do you suppose the O2 will have to say about that?

IMO, for Idle, with a big street-cam, there are just too many variables. I just stopped using that thing for idle.
 
Lots of good info above.....

I can't believe drivability isn't out the window with a 10 drop in the primaries.
 
What heat range are the plugs? Should be NGK 5s. Too cold will look like post #1.
 
I occasionally like to drive it hard. I bought the afr meter to get most out of the new carb. And if I could get better fuel mileage that would be a bonus.

Im aware that afr meter might show falsely reading in idle with big cam overlap. I tuned idle mixture with vacuum gauge to get maximum vacuum. At that point afr meter shows 12.5 to 12.7. Any leaner than that idle quality start to get worse.

At 3000 rpm cruise speed AFR is 14.5. At slow speed steady driving around 2000 rpm afr gauge shows 13.3

Here is more info what you asked:

-Plugs are about 2 year old. NGK BCPR6E
-Electric choke is working properly
-Have not cleaned up any passages in carb. Just visually inspectetd inside that there is no debris or anything
-Idle air jets 70
-High speed air jets 31
-No emulsion jets. Just 4 empty threaded holes in metering block.
-Idle fuel restrictor jets are at the top of metering block. Had not any markings so I dont know what size they are.
-T-slot expossure, have not yet looked up.
-o2 sensor is maybe 5 to 10 inch from collector.

-PCV is in use
-Timing 20 at idle. Total timing 35. All in at 2500 rpm. Plus vacuum advance 7.

Engine is 360. 10:1 compression ratio
RHS iron heads from IMM
Comp Cams extreme energy 244 at 0.050" https://www.compcams.com/xtreme-energy-244-252-solid-flat-cam-for-chrysler-273-360.html
RPM intake
shorty headers
 
Dusterguy said:
I occasionally like to drive it hard. I bought the afr meter to get most out of the new carb. And if I could get better fuel mileage that would be a bonus.

Im aware that afr meter might show falsely reading in idle with big cam overlap. I tuned idle mixture with vacuum gauge to get maximum vacuum. At that point afr meter shows 12.5 to 12.7. Any leaner than that idle quality start to get worse.

At 3000 rpm cruise speed AFR is 14.5. At slow speed steady driving around 2000 rpm afr gauge shows 13.3

Here is more info what you asked:

-Plugs are about 2 year old. NGK BCPR6E
-Electric choke is working properly
-Have not cleaned up any passages in carb. Just visually inspectetd inside that there is no debris or anything
-Idle air jets 70
-High speed air jets 31
-No emulsion jets. Just 4 empty threaded holes in metering block.
-Idle fuel restrictor jets are at the top of metering block. Had not any markings so I dont know what size they are.
-T-slot expossure, have not yet looked up.
-o2 sensor is maybe 5 to 10 inch from collector.

-PCV is in use
-Timing 20 at idle. Total timing 35. All in at 2500 rpm. Plus vacuum advance 7.

Engine is 360. 10:1 compression ratio
RHS iron heads from IMM
Comp Cams extreme energy 244 at 0.050" https://www.compcams.com/xtreme-energy-244-252-solid-flat-cam-for-chrysler-273-360.html
RPM intake
shorty headers
Click to expand...

As Bewy pointed out you are a range cold on plug.

Are the numbers you are giving numbers YOU measured or are they from the web?

You can NOT trust those numbers and no one can give you any advice without knowing exactly how the carb is tuned right now.

Im assuming you have no brass in the emulsion holes. That means you have four open holes. That’s insane. You can’t even behind to tune that.

You also need to determine the size of the hole in the emulsion stack. I’ve seen, from Holley right out of the box as small as .024 (which may not be bad) to as large as .034 and that’s too big for anything I’ve ever tuned.

Also, you need to plug the second hole from the top and the bottom hole for starters. And you have to verify what size the holes are.

You need to verify all the bleed sizes. They could be anything so verify.

You will almost 100% of the time need to take the idle feed restriction out of the upper hole it’s in and move it to the bottom.

You never want the idle feed jet not have fuel above it.

That will get you started but you need to verify what exactly you have. Then you can figure out what to do. Outside of that it’s all guesses.

Edit: your all in by 2500 timing curve is killing power.
 
Dusterguy said:
All numbers are what I have personally measured. Except cam degrees.
Click to expand...

Ok, so what size are the emulsion holes?

If you are just watching an AFR gauge and not data logging you won’t see the negative affects of too many emulsion holes open or too big of holes or both.

You will never see it on a gauge because the resolution won’t show it but what you end up with is (this would be looking at your AFR on a graph) you will see the line saw tooth all the time.

What that means is you can have your AFR could be (I’m making up numbers here but the result is the same) as high as 14:1 and as low as 12:1 in a short (relatively speaking) dyno pull.

We know from data logging in a car the exact same thing happens.

I used those numbers because I have personally seen it that bad.

Also, just so I’m clear did you use pin gauges or drill bits to check the sizes or are you going off the papers that came with it?
 
What is the engine build ? Super efficient chambers ?
Possible too big of power valve restrictors ?
Just thinking out loud here.
 
I dont have pin gauges yet or measured the empty emulsion holes. Air bleeds were marked with numbers but IFR jets and "powervalve jets" were not. Actually I made my own datalogger with Arduino that took afr reading 10 times per second. I try to find the log file and see if its showing something what you described.
 
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Dusterguy said:
I dont have pin gauges yet or measured the empty emulsion holes. Air bleeds were marked with numbers but IFR jets and "powervalve jets" were not. Actually I made my own datalogger with Arduino that took afr reading 10 times per second. I try to find the log file and see if its showing something what you described.
Click to expand...

You might not see it at 10 samples a second or it may not be as clear.

I sample at 50 times a second and I want to try 100 but that may just get too muddy to use.

I’ll go back and look at the sizes you have verified and see.

Also, I can’t emphasize how important for idle quality that you put the idle feed restriction down. Just doing that will do wonders for your idle.

Also, I forgot to mention why having all that emulsion open is so bad.

Those bleeds allow air into the main well. As you add air to fuel it gets lighter and therefore it takes less pressure differential across the booster to get fuel moving up the well and out to the booster.

If you get too much emulsion you will get what’s called “slugging”. That’s why you see the saw tooth AFR curve.

As you introduce more or bigger air bubbles into the main well (or both too many open and too big) eventually they will coalesce into a big bubble. When that happens you get a big “slug” of air. Then you get a big slug of fuel.

And it continues and you see that in you saw tooth graph.
 
Dusterguy said:
I occasionally like to drive it hard. I bought the afr meter to get most out of the new carb. And if I could get better fuel mileage that would be a bonus.

Im aware that afr meter might show falsely reading in idle with big cam overlap. I tuned idle mixture with vacuum gauge to get maximum vacuum. At that point afr meter shows 12.5 to 12.7. Any leaner than that idle quality start to get worse.

At 3000 rpm cruise speed AFR is 14.5. At slow speed steady driving around 2000 rpm afr gauge shows 13.3

Here is more info what you asked:

-Plugs are about 2 year old. NGK BCPR6E
-Electric choke is working properly
-Have not cleaned up any passages in carb. Just visually inspectetd inside that there is no debris or anything
-Idle air jets 70
-High speed air jets 31
-No emulsion jets. Just 4 empty threaded holes in metering block.
-Idle fuel restrictor jets are at the top of metering block. Had not any markings so I dont know what size they are.
-T-slot expossure, have not yet looked up.
-o2 sensor is maybe 5 to 10 inch from collector.

-PCV is in use
-Timing 20 at idle. Total timing 35. All in at 2500 rpm. Plus vacuum advance 7.

Engine is 360. 10:1 compression ratio
RHS iron heads from IMM
Comp Cams extreme energy 244 at 0.050" https://www.compcams.com/xtreme-energy-244-252-solid-flat-cam-for-chrysler-273-360.html
RPM intake
shorty headers
Click to expand...


I quoted this post again so I don’t have to keep going up and looking at it on my phone.

The 70 idle air bleed may be fine depending on what size your idle feed jet it, or restriction as that is used interchangeably.

IMO that MAB is way too big. IMO .026 is a better starting point.

What happens is that big main air bleed will start the booster sooner and then you get rich because you have too much overlap between the main circuit and the transfer slots.

A smaller MAB will delay the start of the boosters.

FYI the MAB has an opposite effect on WOT on the main jet.

The smaller MAB will be richer at the same jet size than a larger MAB. So the MAB affects both low speed (low air flow) fueling and high speed (high air flow) fueling but in opposite ways.

In other words when you go to a smaller MAB you will be leaner at low air flow and richer at high air flow.

A bigger MAB will be richer at low air flow and leaner at high air flow.
 
plot.jpg

Here is graph from datalog. It was 2. gear wot acceleration from 2000 to 6000. Datalogger wasnt working properly because it took samples only 4 to 8 times per second.

I have newer played with air jets or emulsion jets before. Lot of new information to think. I appreciate your input.
 
P
Dusterguy said:
plot.jpg

Here is graph from datalog. It was 2. gear wot acceleration from 2000 to 6000. Datalogger wasnt working properly because it took samples only 4 to 8 times per second.

I have newer played with air jets or emulsion jets before. Lot of new information to think. I appreciate your input.
Click to expand...


THANK YOU for posting that graph.

One look at it and I’d have told you that you have too much emulsion. That’s what it looks like when they start slugging.

Even at 4-8 samples you can clearly see it.

Keep logging stuff. It won’t be long and you’ll be a real good carb tuner.

You can charge for that except the hard part is convincing some folks they need their carbs corrected.

Most excellent work!

Edit: at the beginning you can see about 13:1 and then it drops to a bit over 10:1 in that short of time. When I first saw that I couldn’t believe my eyes.
 
Not sure what happens at beginning. Acceleration pump seems to have its own issues, when I press gas lightly at any speed it goes momentarily leaner and after that start to accelerate properly.
 
mbaird said:
What is the engine build ? Super efficient chambers ?
Possible too big of power valve restrictors ?
Just thinking out loud here.
Click to expand...
Jeez… I really need to read the thread better before posting .
Sinility is setting in …lol
 
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