Tuning Carb With An Air/fuel Meter.

Chevyjet52 · November 23, 2009

I recently bought and installed a wideband air fuel ratio kit which consists of the O2 sensor, computer and a dash mounted gauge. I need advice on how to tune the carb using the meter.

I have Jeep Wrangler with a 350. It has a Holley Avenger truck carburetor. It runs pretty good right now, but I can tell it's a little on the rich side.

I haven't touched anything on the carb yet, just want to make sure before screwing around with it.

What RPM is best for tuning? I've noticed the reading on the gauge moves around quite a bit while driving. (sometimes below 12 and above 14)

Do you simply turn the mixture screws to adjust the A/F ratio?

Most of my driving is slow since the Jeep is used mostly for trails, it's not a daily driver. Rpms rarely get above 3000.

redvett · November 23, 2009

The idle circuit works until about 1600-RPM's that can be adjusted with the idle screws, the hi speed or main jets are removable and can be changed as needed.

Chevyjet52 · November 23, 2009

The idle circuit works until about 1600-RPM's that can be adjusted with the idle screws, the hi speed or main jets are removable and can be changed as needed.

Thanks for replying,

What's the target ratio for the idle circuit?

Nytemare · November 23, 2009

Ideal is 14.7 for everything...but your not going to have that everywhere. 12.7-13.3 is optimal power.

You should tune it at low idle, with the low screw. Than bump the idle to around 2000 and tune again with the high screw.

That's how I used to do it anyway...but that was years ago.

It wont be as simple as turning 2 screws once either. You are going to be going back and forth between idle and 2k to get both set as close as possible...and you may have to re-jet to get the optimal ratio.

desrtrat · November 23, 2009

Ideal is 14.7 for everything...but your not going to have that everywhere. 12.7-13.3 is optimal power.

You should tune it at low idle, with the low screw. Than bump the idle to around 2000 and tune again with the high screw.

That's how I used to do it anyway...but that was years ago.

It wont be as simple as turning 2 screws once either. You are going to be going back and forth between idle and 2k to get both set as close as possible...and you may have to re-jet to get the optimal ratio.

another thing that is critical is your float level. a c**t hair to high or to low will affect your over all a/f ratio. when making your final idle adjustments, use a vacuum gauge. set idle to spec, adjust your 2 air/fuel screws to achieve the highest vacuum, then reset to final idle rpm..this sounds confusing but very simple

good luck