nastee383

I installed an air/fuel ratio guage and in general terms this is how my car runs. Tell me if this is right or should it be different. According to the gauge the car idles in the yellow (stoich), cruises in the red (lean) and is rich (green) under WOT. I have a Q-Jet with 77 primary jets and 47 primary rods. I also have a second Q-Jet I use with 71 primary jets and 51 primary rods. It runs the same air/fuel ratio AND gets the same mileage. My understanding is that some Q-Jets were designed to run lean at cruise. 75's and later with APT. One is my original '75 and the other is a 1980. Both have been redone by The Carb Shop. I have full time fresh air induction and Hooker sidepipes which may or may not contribute to the lean cruise. Tell me what you think.

1979toy

I would think that you would want green at all throttle settings.
I've got to get a bung welded on my exhaust so I can tune my own.

Matt Gruber

it only has 3 LED's?...
mine has 10
i can't imagine tuning with only 3.

Bob D

You engine is designed to run lean at partial or "cruise" blade openings. This is normal. However, by making modifications to the exhast system so that it scavages better, you are actually leaning out the fuel/air mixture further. If you don't have ping at partial setting with a load then you should be OK.

Nearly all power modifications to an engine are either increasing the fuel/air charge entering the cylinder or to make better use of the charge that arrives. Carbs, intake, head passage mods/design, cam, valves, exhast all work to move more air/fuel. While higher compression ratio's via piston domes and smaller head pockets tend to make better use of the charge.

All that said, I believe that if you're really interested in this subject there are digital meters that will translate the data into numbers. They are somewhat more expensive than the consumer market gages, but are more accurate and provide information rather than an indication. There are two basic types - the first measures the air/fuel density in the intake manifold/ports and the other measures the exhast gases. Advanced dyno's use both to see the effects of any modification. Hope this helps.

Bob

nastee383

It has three sections with several LED's per section. It's the "Autometer" gauge.

Matt Gruber

WOT and idle 12.9-13.1
Cruise = as lean as possible without surging

to calibrate see my article http://community.webtv.net/MATTGRU/AFtesting