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AFR readings?

Ad B

Ad B

Cruisin' Guzzisti
GT Contributor
Joined
Nov 7, 2010
Messages
279
Location
Sint Oedenrode
Hi Guzzista,

I’ve read a bit of the techniques of the Guzzi (Griso 1200) here and in books.
I’ve been looking in and around the bike how it works, what it is etc..
The Guzzi also made a visit to a powerbench to see how it performs
and try to adjust his injectionmapping for a better torque curve and performance.
This all succeeded.
But because the AFR sensor was blown half out of the exhaust with his final and best run,
we haven’t a AFR result with the last run.
Now I have bolted a AFR gauge on the bike to see how the AFR behaves.
It’s on the bike just a few minutes now. It works, but I didn’t drive on the road yet.
I asked myself and with this topic to you, why is it that the AFR number we are talking
about on this forum is 13 for the best mixture??
And the ideal number is 14.7 for a petrol burning car and bike.
According the chemists on the net and Wikipedia.
The numbers of the gauge I have let me see that the numbers 13 to 17 for a optimal mixture.
Les is too rich, more is too lean.
How must or can I see and feel these numbers?
When is the mixture too rich or too lean? When is it starting to get dangerous at the lean side?
Help me to learn, learn without damaging my bike and pride… :mrgreen:

Thanks for your input.
Ad B
 
good questions, i'm curious as well.

a guess as to why 13:1 is recommended for Guzzi instead of the typical 14.7:1 is because it's air cooled? running slightly rich seems it would be better than running any lean with an air cooled engine. running a little lean would probably damage an engine more than an engine running a little rich. i could be wrong...
 
This simple graphic should explain everything... this is based on the ranges for an air-cooled engine for power and cooling. The below graph (blue trace) is of a stock Norge at 20% throttle (which is about where most average when cruising ~15-10%).
 

Attachments

  • Norge20-AFR.jpg
    Norge20-AFR.jpg
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A quick note to add to the discussion.
14.7 to 1 is the ideal ratio for complete burn. It is typically not the ideal for max power. That number is usually lower (richer) but varies depending on the motor. Air cooled vs. water cooled, combustion chamber design, lots of factors play into this. The ideal ratio also varies depending on whether the rpms are quickly increasing (accelerating in lower gears) or slowly increasing (near flat out in top gear).
14.7:1 is simply the ratio where the fuel and air is mixed so that there is enough air to burn all the fuel. Maximum efficiency. Max power or cooler running may require a different ratio.
 
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