Carb tuning with narrow band sensor?

[Metal Man]

I have a edelbrock narrow band sensor I am going to install to see if I can tune my engine a little better. I had it on before and the sensor showed that acceleration WOT was pretty much right on but as soon as the truck stopped accelerating and smoothed out all the lights on the sensor would go out. I do not have a lean surge of any kind at this time but I believe that I am running on the edge of or am running lean during cruise. The truck is a daily driver 350 sbc , fresh rebuild to stock specs. running a catalytic converter and stock muffler.

[Cliff Ruggles]

Doesn't necessarily mean that's it's lean.  If the engine is happy, that's all that really matters.  As long as the engine is smooth off idle, not surging, bucking, kicking, lacking power, etc, then it's fine. 

In any and all cases, tune A/F for what the engine wants, and then check it with an A/F meter to see where you are at?.....Cliff

[Metal Man]

Thanks I appreciate the help. I took the truck out for a spin earlier and heres what I came up with.

Turn the truck on , let it run for about 5 minutes to make sure sensor is hot, choke is engaged, and the LED's go to the last red on the right and goes out. LEAN
I take the choke off and idle and the LED's  light all up coming from the right hand side and stop at 12.5
Accelerating on to the highway , slow and steady acceleration LEDs are lit up from the right to the 13 bulb. RICH
WOT, and the bulbs are lit up from the right to the 12.5 mark. RICH
Letting off the gas completely after WOT and I get 12.5. Rich


I am thinking I should start with my jetting, to get WOT around 14.7 then start on the cruise circuit?

[Metal Man]

scratch that 14.7 got a little confused there.

[Metal Man]

I am a little confused in the idle circuit . The meter shows that i am rich at idle, 12.5, and lean on the cruise circuit, no lights higher than 15. These two controlled by the APT screw, primary rods? So If I want to lean out the idle do i need to install idle down tubes with a smaller restriction to lean out the idle? Also raise the APT screw , or smaller primary rods to richen up the cruise?

If so do you sell stock idle down tubes? I know you have the primary rods.


I have adjusted the APT screw some and it runs better and idles better than before even thought the meter is telling me that I am off. I can see where you say to adjust it to what the motor like and not follow the meter. I have a slight miss that I cant track down , very slight. It has almost disappeared at idle with my current settings. All parts on the engine are new including dist.

[Cliff Ruggles]

Idle mixture is set with the mixture screws, for best idle quality.  Doesn't matter what the meter says, turn the mixture screws in till the engine slows slightly, then back about 1/4 to 1/2  turn.  This will be the A/F the engine wants at idle.

Do the "tip-in" test to set the APT.  Shoot for about 100-150rpm's increase during tip-in, this will be a good starting point, and on the edge of lean for what the engine can tolerate.  Once again, doesn't matter what the meter says, this is what the engine wants.

Drive the truck, do some heavy part throttle runs, and full throttle runs.  Engine performance should be smooth and good power at all levels.  If it acts anemic anyplace, look at where your gauge is at to determine if it needs more or less fuel at any level.

Larger jets are required to fatten up the primary side only, secondary metering rods for full throttle, once you have determined the ideal jets to use.

What is the carburetor number, and what has been done to the carburetor?......Cliff