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post #1 of 3 (permalink) Old 04-30-2017, 03:33 PM Thread Starter
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AFR ratios

I'm trying to wrap my pea brain around the AFR number with the tuners. Maybe someone here can turn the flashlight on?

Would it be fair to say that there is an optimum AFR number? Wouldn't that number apply to all riding scenarios? Would the number be a variable, based on what your riding like at the time.

If the number is perfect at 14.7 (ie complete burn), is this "lean"? Where does lean turn to rich? In a map does one tweak AFR for a range to get fuel economy where it should be?

Reason for ?s is when I first started the 'Autotune' on the FP3 the mileage was terrible but has come back to what it was like before the mods. The AFR tables look very similar, are these not what changes?

If this is a pain in the @#$, just say so

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post #2 of 3 (permalink) Old 04-30-2017, 03:41 PM
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Stock AFR is 14.7 and it is considered lean by some but it helps the bike meet EPA reg's and it also makes the bike get fairly good mpg. Some tuners want to drop the AFR down into the 12's which helps the bike run a little cooler but it will also drop the mpg's into the low 30's or high 20's. I set my AFR around 14 which richens the bike and will keep the mpg's around 40. Try keeping the AFR between 13.5 and 14 and everything should be OK. JMO

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post #3 of 3 (permalink) Old 04-30-2017, 03:50 PM
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14.7:1 is stoichiometric for pure gasoline. Today gas has up to 10% Ethanol, so that number is actually a little off. For a street Twin Cam on pump gas the tunes usually end up around 14.0 to 13.8:1 In round numbers best power was around 12.5:1 and best fuel economy was 15.5:1.

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