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Old 02-10-2013, 01:36 AM
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You do not need to target a afr when ideling. The priority is idle quality.
the engine will idle best with a AFR that is slightly richer than 14.7:1
what ever give the best idle quality. Use a manifold vacuum gauge to set the idle .
off idle low cruise 14.7:1 +/-

Cruise at part throttle 14.7:1 +/-.... a bit leaner saves a bit on fuel over distance.
The limit is leanest cylinder misfire and heat. Lean needs more timing (vac adv)
don;t get all carried away. 15.7:1 +/-

Primarily on the primary main jets.

As you step into the throttle further and power the AFR should progressively shift richer.

The power valve opening point sets the transition point from cruise to power mode.

WOT Power 13.8 to 12.5:1 Being on the rich end of this helps keep things cool @ WOT
Supercharged WOT power is often tuned richer than this to avoid detonation/ and priignition . 10.5:1 to 12.5:1 as required.
There is a limit to have far this will get you. afer than, more is not better. its worse.

A afr gauge only reads the average of the cylinders. They are not all the same.
You are always tuning for the worst cylinder. A afr gauge does not read the actual AFR. it reads oxygen in the exhaust.
The AFR is a assumption based on this amount of oxygen sensed in the exhaust. Not always accurate.
exhaust leaks and ignition misfire make the gauge leaner.

Last edited by F-BIRD'88; 02-10-2013 at 01:48 AM.
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