AFR Gauge Confusion

[Mlcdc1]

Trying to set up an Edelbrock 1906 on 1977 GMC with 350 (all stock) and confused about what AFR gauge is telling me. At idle (750 rpm) it reads anywhere from 12-12.6. At cruising, (1800 rpm @ 60mph) it reads 14.2-15.0. I have not been able to get close to 14.6 at idle by changing rods in the carburetor. It seems to run great at cruising speed with any issues. Any suggestions or help would be appreciated. Thanks.

 

[Camar068]

not that I know about AFR tuning, but what pressure are you running to the carb? If your over 5-6 psi, it's too high.

I had a 1406 and wanted to dial it in but have since done the LS swap. If I had to do it again, I'd go with an electric fuel pump to get steady pressure instead of pulsing (can see it on a gauge with a mechanical pump). That way you now exactly what your pressure is instead of pulling an average.

Anyway, hope this helps.

 

[Mlcdc1]

Thanks for the input. I’m running 4.5-5 of fuel pressure.

 

[ali_c20]

The main rods and jets do not effect idle. Idle is adjusted with the idle mixture screws and the idle speed screw ( air screw).

This is from the Edelbrock manual:

IDLE MIXTURE

The Edelbrock Performer Series carburetor has conventional Idle Mixture Screws (IMS) that provide a leaner A/F when turned clockwise and richer A/F when turned counter clockwise.
The idle air flow is controlled by a conventional screw that opens the Primary Throttles.
The following procedure should be used to set the idle mixture and speeds

1. Fully warm engine and ensure choke is fully open.
2. Air cleaner in place.
3. Set desired speed with the air screw.
4. Adjust the IMS on ONE side to get the maximum possible RPM.
Do not go rich beyond the maximum speed point.
5. If the above changed the idle speed more than 40 RPM, then readjust the speed.
6. Adjust the side OPPOSITE of that in Step 4 to get maximum RPM
7. Reset the speed.
8. Carefully trim each IMS to again get the maximum idle RPM.
9. Go leaner just enough to get a 20 RPM drop in speed.
10. Reset the speed to the desired RPM.
11. This is a Lean-Best Idle Set. Setting richer than this will not
improve idle quality or performance, but could tend to foul plugs.