AFR Tuning
Diagnostics

Start it and let everything warm up, the engine and the sensor both. The gauge reads in zones, and the sensor voltage under it tells you which side of perfect you are on: down under about a third of a volt is lean, switching around the middle is right at the balance point, and up over six-tenths is rich. A narrowband sensor cannot hand you an exact ratio; what it hands you, zone by zone, is the truth about which side you are on, and for jetting work that truth is enough to steer by.

Work the throttle in zones, because each zone answers to a different control, and the page's target band moves with the zone. At idle, the mixture screw is the tool. Turn it in small moves, out for richer, and give the trace a few seconds to settle after every move before you believe it. Just off idle, the pilot jet feeds the fire; if your screw ends up turned way out past about three and a half turns and the zone still reads lean, the pilot is too small and the screw is telling you it wants a bigger one.

Cruise belongs to the needle. A clip moved one groove lower raises the needle and richens the middle. One groove at a time, then ride it or hold the zone and re-check. Wide open belongs to the main jet, the last quarter of the throttle; a bigger number feeds more fuel up top.

One change at a time. That is the entire discipline. Change two things and the gauge can only tell you the sum, and you will never know which one did it. Zone by zone, one control, small moves, let it settle, write down what you did. When every zone sits in its band through a steady hold, the popping, the flat spots, and the sooty plugs have nowhere left to hide.

Let me walk you down the screen. At the top is the gauge. Start the engine first. Pick a throttle zone with the throttle slider, and the gauge shows your air fuel ratio, your lambda, and the target for the zone you are in. That target is the lesson at the heart of this page: the band moves with the zone. A number that is perfect at cruise is dangerously lean at wide open, so the page never judges you against one fixed number.

Under the gauge, the sensor's own language: under about three tenths of a volt reads lean, switching around forty-five hundredths is stoich, over six tenths is rich. Right below sits the guidance box. Once the engine is running, this box names the exact control for the zone you are in, mixture screw, needle clip, or main jet, and which way to move it. Crack the throttle open fast and you will see the needle dip rich for a beat. That is the accelerator pump shot, just like the real carb.

Now the Jetting section, and here is the discipline: each control owns one part of the throttle range, and you change one thing at a time, then re-check. The idle mixture screw owns idle. Out, counterclockwise, is richer, and your baseline is two and a half turns out. The pilot jet feeds idle and the first crack of throttle. If the mixture screw ends up past about three and a half turns and it still runs lean, the pilot is too small. The needle clip owns the cruise zone. A lower groove raises the needle and richens the midrange, one groove at a time. The main jet owns wide open, the last quarter of throttle, and a bigger number is richer. That is the one the dyno settles.

Under the controls, the Live trace draws your last twelve seconds against the target band. A steady line inside the band is the goal. Hunting at idle and a sag when you crack the throttle both show up here first.

Your jetting settings save on this device, so the page remembers your setup between sessions. And at the bottom, Trends. With Premium, the page logs your cruise reading every session and watches it drift. One reading can lie. A trend cannot. That is the page. Start the engine, pick a zone, and let the guidance box tell your hands what to do.