#1  
Old 05-28-2022, 04:57 PM
Paulryder Paulryder is offline
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Default Adjusting air/fuel ratio with AEM UGEO gauge

I installed an AEM X-series Universal Exhaust Gas Oxygen (UGEO) gauge so that I can set my air/fuel ratio on my 1966 GTO Tri-Power center carb for the best power and torque. Initially I set the idle mixture screws so that I had a reading of about 14.6. I have since backed the screws out to 5 and 1/2 turns and the lowest reading I can get is around 13.3. I would like to get to 12.5 or so for the best power. Once I tried going any further out (to 6 or 6 and 1/2 turns), the screws feel pretty loose and the mixture is not changing anymore. Is there something else I need to adjust or change in order to get a richer mix?

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Old 05-28-2022, 07:06 PM
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Tom Vaught Tom Vaught is offline
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Idle Mixture has very little to do with best power.
Totally different circuits.
You should have left the idle screws where they were when you were at 14.6 or maybe as low as 14.2 on the idle air fuel ratio.

Easiest way to the the proper air/fuel settings on the center carb is to send the center carb to Dick Boneske (who does a LOT of work on Tri-Power set-ups) and have him set it up for best power and mid range.

If you do not understand the given circuits and how to manage them PROPERLY you are wasting your time. He could also send you jets for the front and rear car for the max power parts of the HP curve.

Tom V.

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  #3  
Old 05-28-2022, 07:41 PM
Paulryder Paulryder is offline
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Quote:
Originally Posted by Tom Vaught View Post
Idle Mixture has very little to do with best power.
Totally different circuits.
You should have left the idle screws where they were when you were at 14.6 or maybe as low as 14.2 on the idle air fuel ratio.

Easiest way to the the proper air/fuel settings on the center carb is to send the center carb to Dick Boneske (who does a LOT of work on Tri-Power set-ups) and have him set it up for best power and mid range.

If you do not understand the given circuits and how to manage them PROPERLY you are wasting your time. He could also send you jets for the front and rear car for the max power parts of the HP curve.

Tom V.
Hmmm... Maybe you can watch this video and explain further?

https://youtu.be/EY78uPXvvY0

  #4  
Old 05-30-2022, 10:38 AM
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Tom Vaught Tom Vaught is offline
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The video explains basic air/fuel values for different mixtures.

It said nothing about what each carb circuit did, when it did it, how it did it, and what the effect would be on the total air/fuel curve that the engine sees in the different modes of operation.

The video DOES tell you how to understand the air/fuel numbers that are being displayed on your AEM X-series Universal Exhaust Gas Oxygen (UGEO) gauge.

In simple terms: it is a cold day outside, the front door is wide open, you go into the bathroom and close the door. Yep it might be warmer in the bathroom vs being in front of the open front door (but you really did not fix the problem. You avoided the problem or did not understand the problem where the fix was to close the open front door.

That applies to your adjusting the idle mixture screws trying to tune the midrange circuits on the carburetor.

Idle circuits are for IDLE and Off-idle fueling requirements when the throttle blades are barely open. Not when you are cruising down the road at higher throttle blade angles.

Hope that helps.

Again, My recommendation, send the carb to Dick Bonesky and you will be a lot happier.
Then you can read the air/fuel ratio numbers when the carb is tuned correctly for your engine.

Tom Vaught

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  #5  
Old 05-30-2022, 01:23 PM
Paulryder Paulryder is offline
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Quote:
Originally Posted by Tom Vaught View Post
The video explains basic air/fuel values for different mixtures.

It said nothing about what each carb circuit did, when it did it, how it did it, and what the effect would be on the total air/fuel curve that the engine sees in the different modes of operation.

The video DOES tell you how to understand the air/fuel numbers that are being displayed on your AEM X-series Universal Exhaust Gas Oxygen (UGEO) gauge.

In simple terms: it is a cold day outside, the front door is wide open, you go into the bathroom and close the door. Yep it might be warmer in the bathroom vs being in front of the open front door (but you really did not fix the problem. You avoided the problem or did not understand the problem where the fix was to close the open front door.

That applies to your adjusting the idle mixture screws trying to tune the midrange circuits on the carburetor.

Idle circuits are for IDLE and Off-idle fueling requirements when the throttle blades are barely open. Not when you are cruising down the road at higher throttle blade angles.

Hope that helps.

Again, My recommendation, send the carb to Dick Bonesky and you will be a lot happier.
Then you can read the air/fuel ratio numbers when the carb is tuned correctly for your engine.

Tom Vaught
Thanks for taking the time to respond and for the explanation. I didn’t say it up front, but my main goal is to achieve the best overall performance from my 389 that I can without modifying anything, i.e. not disassembling things and sending them off. Besides looking at the carbs and adjustments I can do to them, I’m also exploring adjustments of ignition timing that I can make that might improve performance. I’m not looking for monumental gains here, my thoughts in all this are, if I can improve performance in any way, no matter how slight, by making adjustments only, then it’s a win. The other prominent goal is that I learn things along the way. I will also mention that my center carb was recently restored by Mike Wasson at Pontiac Tri-Power.

  #6  
Old 05-30-2022, 01:33 PM
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If it was restored by Mike Wasson, then you should have left it alone vs mess with it and the center carb blade position vs throttle screw position and transfer hole position in my opinion.

The position of the throttle blades is very important, be it a Rochester 2-BBL carb, a AFB carb, or a Holley carb.
But it is what it is. Have fun playing with it.

Tom V.

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  #7  
Old 05-30-2022, 02:45 PM
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Tom Vaught Tom Vaught is offline
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It amazes me that people spend their hard earned money on carb work, and then buy a
air/fuel gage and think they can do better vs a carb expert with years and years of experience.
But it is what it is, good luck sir. I am done on this one.

Tom V.

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  #8  
Old 05-31-2022, 07:22 PM
Goatracer1 Goatracer1 is offline
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People now days kill me. You can get a perfectly acceptable idle using nothing more than your eyes and ears when working on these old cars. That's how we did it when they were new and it will work just as well now. If you want to get really technical use a tachometer and a vacuum gauge. Adjust idle screws for highest (best) idle vacuum and set RPM with the tach.

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