With a closed-loop system, the ECU checks the air-fuel ratio against the target numbers, but now the computer uses that information to adjust the fuel delivery to meet the target air-fuel ratio. The tuner also has the option of adjusting the correction factor and also switching between open- or closed-loop.
Power output is a function of air-fuel ratio and ignition advance. Air- fuel ratio and ignition advance will also influence EGT and knock count. For an engine to be thoroughly calibrated or “tuned”, its efficiency should be optimized at all engine speeds. The A/F and ignition timing settings that deliver the maximum torque at a specific RPM
Well, maximum power is generated at an AFR of 12.6:1, so you may be too lean at 12.8-13.2:1. You may want to shoot for 12.0-13.0. Best fuel economy is given at 15.4:1 so deceleration should probably be 15.0-16.0. Ideal stoichiometric AFR is 14.7:1 but in practice that is a tad lean for idle.
after 3 passes N/A on a new motor i had a best et of 12.7 .with a A/F of 12.9:1 at 28 deg timing .jetted 50 shot and dropped to 12.1 et with a A/F of 11.9:1 , leaned it out by dropping fuel pressure and ran 11.7 et with a A/F ratio of 13.0:1 when i pulled or added timing et dropped so 28 deg was the ticket for that jetting . hope it helps.
The air-to-fuel ratio refers to the amount of air and fuel mixture supplied to the engine for combustion. It is typically expressed as a ratio, such as 14.7:1, which represents the stoichiometric ratio for gasoline engines. This means that for every 14.7 parts of air, 1 part of fuel is required for complete combustion.
This is what I should try to achieve; Idle 12.5 to 13.2, Cruiseing 14.7 to 15, Max Power 12.6 to 12.8. Column 1 is where I started with the A/F gauge. Carb was jetted up from stock. Column 2 is jetting back to stock for the 670. Column 3, leaning the jetting started to improve the ratio.
Blend A/F ratio. = (0.20 E85 A/F Ratio) + (0.80 Gasoline A/F Ratio) = (0.20 9.765) + (0.80 14.7) = 13.713. If you knew for sure the pump gas already contained 10 percent pure ethanol (E10 in the
MruH1i.
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    • how to tune air fuel ratio