How to tune using air & fuel ratio gauge - JeepForum.com
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post #1 of 59 Old 01-21-2020, 02:30 PM Thread Starter
agear
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So I bought an air fuel ratio gauge for my 84 258 with weber 38 stock exhaust. I know how to set lean best idle . But I'm wondering ; do you have to do anything else other than mess with the mixture screws to get the ratio you want


1984 jeep cj7, 258 I6, rebuilt T176,rebuilt Dana 300, amc 20 , dana 30, 4.10's Trac-lok in rear , 4.10's detroit soft locker in dana 30, 2.5 inch bds suspension lift, 1 inch polyurethan body mount lift. Line ex. weber carburetor. factory tach. factory clock ,oem replacement speedomter cluster, and oil pressure gauge, factory volt gauge.
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post #2 of 59 Old 01-21-2020, 03:20 PM
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post #3 of 59 Old 01-21-2020, 08:35 PM
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Depends on how in-depth you want to get. You could drive it, see where the A/F is at cruise, WOT and see if there is an adjustment. I know carbs like the Q-Jet and Edelbrock have needles that move inside the jet to change fuel flow for different throttle openings.



Basic carbs, you have the idle circuits (screws) and then the main jets for all other driving. Adjusting screws and changing jets are about it. Maybe an accel pump adjustment.

Rick

1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy


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post #4 of 59 Old 01-22-2020, 06:51 AM
Shawn Watson
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How does it look so far at say, 2200 rpm in 3rd gear, just cruising at that speed?


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post #5 of 59 Old 01-22-2020, 11:30 AM
Matt1981CJ7
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Agear,

Which A/F gauge did you get? Are you using the factory O2 sensor bung? I ask because my gauge came with specific instruction to locate the O2 sensor a certain distance downstream from the manifold collector.

I have my warm idle mixture set to about 14:1, and my light throttle cruise mixture at 14.5-14.7:1. I've never been able to dial in the secondaries of my Q-jet, and I've tried all the tricks. The secondaries run way rich if I really mash the throttle, but not bad if I ease into WOT.

The first thing you'll notice is how your ratios will vary slightly from day to day depending climatic changes. They'll even change slightly on an hourly basis, so don't drive yourself crazy trying to maintain exact ratios.

Matt


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post #6 of 59 Old 01-22-2020, 02:11 PM Thread Starter
agear
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I got the same one as shawn. Thanks for the replies. It's still on the way from.summit racing . The only bung I have is on the exhaust manifold just above the flange connecting it to the rest of the exhaust

https://www.summitracing.com/parts/ATM-4379

1984 jeep cj7, 258 I6, rebuilt T176,rebuilt Dana 300, amc 20 , dana 30, 4.10's Trac-lok in rear , 4.10's detroit soft locker in dana 30, 2.5 inch bds suspension lift, 1 inch polyurethan body mount lift. Line ex. weber carburetor. factory tach. factory clock ,oem replacement speedomter cluster, and oil pressure gauge, factory volt gauge.
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post #7 of 59 Old 01-22-2020, 02:28 PM
Matt1981CJ7
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OK, I don't know what brand Shawn has. Anyway, just make sure the factory O2 location works with whatever model you have.

My Innovate A/F meter instructed to install the O2 sensor at least 24" downstream of the exhaust collector, so that it wasn't exposed to excessive heat that could potentially burn the sensor up.

Matt


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post #8 of 59 Old 01-22-2020, 02:29 PM Thread Starter
agear
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Quote:
Originally Posted by Matt1981CJ7 View Post
OK, I don't what brand Shawn has. Anyway, just make the factory O2 location works with whatever model you have.

My Innovate A/F meter instructed to install the O2 sensor at least 24" downstream of the exhaust collector, so that it wasn't exposed to excessive heat that could potentially burn the sensor up.

Matt
https://www.summitracing.com/parts/ATM-4379

1984 jeep cj7, 258 I6, rebuilt T176,rebuilt Dana 300, amc 20 , dana 30, 4.10's Trac-lok in rear , 4.10's detroit soft locker in dana 30, 2.5 inch bds suspension lift, 1 inch polyurethan body mount lift. Line ex. weber carburetor. factory tach. factory clock ,oem replacement speedomter cluster, and oil pressure gauge, factory volt gauge.
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post #9 of 59 Old 01-22-2020, 07:02 PM
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Quote:
Originally Posted by Matt1981CJ7 View Post
My Innovate A/F meter instructed to install the O2 sensor at least 24" downstream of the exhaust collector, so that it wasn't exposed to excessive heat that could potentially burn the sensor up.

That's the one I have also and had to weld in a new threaded bung low on the head pipe.
I set it up to a 14.7:1 air/fuel ratio @ warmed up idle adjusting the mix screws on a NOS Carter BBD. Very little adjustment if any, it was already set out of the box that sat on a shelf for 30 years.

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post #10 of 59 Old 01-23-2020, 08:17 AM
Matt1981CJ7
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Quote:
Originally Posted by keith460 View Post
That's the one I have also and had to weld in a new threaded bung low on the head pipe.
I set it up to a 14.7:1 air/fuel ratio @ warmed up idle adjusting the mix screws on a NOS Carter BBD. Very little adjustment if any, it was already set out of the box that sat on a shelf for 30 years.

Yep, they make tuning a carb very easy. No more vacuum gauges, or guessing by ear, just adjust the screws until the numbers are correct.

I routed my O2 sensor wire thru one of the drain holes in my tub, and have the meter display sitting between the shifters at all times. I find myself looking at the A/F meter more than any other gauge in the Jeep. A while ago, I had a rocker arm fail causing one dead hole in my V8. The immediate rich condition that showed up on the A/F gauge was the first thing that alerted me to the problem.

I honestly think it's a must have tool for anyone who likes to tinker with carb'd vehicles.

Matt
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post #11 of 59 Old 01-24-2020, 07:46 AM Thread Starter
agear
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How do you wire it up ? Do you use a relay and if so which wires go where ?

1984 jeep cj7, 258 I6, rebuilt T176,rebuilt Dana 300, amc 20 , dana 30, 4.10's Trac-lok in rear , 4.10's detroit soft locker in dana 30, 2.5 inch bds suspension lift, 1 inch polyurethan body mount lift. Line ex. weber carburetor. factory tach. factory clock ,oem replacement speedomter cluster, and oil pressure gauge, factory volt gauge.
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post #12 of 59 Old 01-24-2020, 08:04 AM
Matt1981CJ7
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Mine plugs into the cigarette lighter.

I suspect a switched power source is all you need.

Matt


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post #13 of 59 Old 01-24-2020, 09:04 AM
Shawn Watson
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I believe it was keyed power, a ground and tie into your dash lights.


Shawn

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post #14 of 59 Old 01-24-2020, 06:06 PM Thread Starter
agear
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I got the gauge installed. I tried to set it 13.7 idle. But after I did that the longer It idles the leaner it runs

1984 jeep cj7, 258 I6, rebuilt T176,rebuilt Dana 300, amc 20 , dana 30, 4.10's Trac-lok in rear , 4.10's detroit soft locker in dana 30, 2.5 inch bds suspension lift, 1 inch polyurethan body mount lift. Line ex. weber carburetor. factory tach. factory clock ,oem replacement speedomter cluster, and oil pressure gauge, factory volt gauge.
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post #15 of 59 Old 01-25-2020, 06:34 AM
Shawn Watson
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Quote:
Originally Posted by agear View Post
I got the gauge installed. I tried to set it 13.7 idle. But after I did that the longer It idles the leaner it runs
You're going to find a few "weird" things like that in the beginning. My advise would be to holster your tools and spend a week or two getting used to the readings while driving with a smooth foot. Once you start seeing some trends, let us know what they are and we'll see if we can help.

The vast majority of your time will be spent with fuel being delivered from the idle (low-speed) circuit so pay attention to what your readings are when you're just following traffic at normal speed.

I have a feeling you'll soon see why I stopped using 1.5 turns as the cutoff point for mixture screw adjustments. Please refresh my memory on your current jetting and emulsion tubes.


Shawn
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