Thrust issues with AFR gauge and Brawler carb

-
D

Dusterguy

Well-Known Member
Joined
Aug 9, 2011
Messages
235
Reaction score
19
Location
finland
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
 
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.
 
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
 
Last edited:
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.
 
What heat range are the plugs? Should be NGK 5s. Too cold will look like post #1.
 
You must log in or register to reply here.
-

Back
Top