AFR: 44 Opinions

[2002#3]

While tuning dual Solex 40 PHH's over the last month or so, I constantly referred to our FAQ and a few other sites to determine recommended AFR's for different RPM's, stages of carb performance, speed, acceleration, carb load, etc.  I found a lot of good info, mostly on FAQ (thanks, contributors).  The recommendations/suggestions/opinions were numerous and varied.  In my visually oriented mind, I needed a visual and tangible compilation of the 44 recommendations I recorded (there were many more I did not record) to determine a reasonable (average?) range for my carbs as a reference.  See attached below.

• Each entry is a single recommendation.  Some entries were suggested by several contributors but were recorded only once.
• The overwhelming majority of recommendations were for Webers.
• Values for instant and full acceleration are not included (usually 10 to 11).
• Some contributors used "full power" instead of WOT.
• Commonly, each contributor provided explanations and discussions of their recommendation(s).
• Most contributors suggested using suggested AFR's as a guide, getting them close to reference values, and then adjusting for good performance.

Maybe this info will be helpful to those of you who, like me, are learning to be friends with carbs.

NOTE:  Thanks so much, Ed Zinsmeyer, for your superb and valuable help re: AFR's and my Solexes.

 

Larry

[man_mark_7]

53 minutes ago, 2002#3 said:

While tuning dual Solex 40 PHH's over the last month or so, I constantly referred to our FAQ and a few other sites to determine recommended AFR's for different RPM's, stages of carb performance, speed, acceleration, carb load, etc.  I found a lot of good info, mostly on FAQ (thanks, contributors).  The recommendations/suggestions/opinions were numerous and varied.  In my visually oriented mind, I needed a visual and tangible compilation of the 44 recommendations I recorded (there were many more I did not record) to determine a reasonable (average?) range for my carbs as a reference.  See attached below.

• Each entry is a single recommendation.  Some entries were suggested by several contributors but were recorded only once.
• The overwhelming majority of recommendations were for Webers.
• Values for instant and full acceleration are not included (usually 10 to 11).
• Some contributors used "full power" instead of WOT.
• Commonly, each contributor provided explanations and discussions of their recommendation(s).
• Most contributors suggested using suggested AFR's as a guide, getting them close to reference values, and then adjusting for good performance.

Maybe this info will be helpful to those of you who, like me, are learning to be friends with carbs.

NOTE:  Thanks so much, Ed Zinsmeyer, for your superb and valuable help re: AFR's and my Solexes.

 

Larry

 

Wow. This is a great piece of work. You save me so much time. One question - why are there gaps in the WOT bars? For example, the very first row is solid from 12.5 to 13, then there is a gap, then a solid bar again from just below 13.5 to just above 13.5.

 

thx

mm

[jp5Touring]

Wow is right. Just when I thought I was understanding my Weber 40's. ?

More info to confuse me even more.  Very Cool...

[uai]

for me it's too complicated - if it runs good and isn't lean I'm fine.

The final ±005 on mains or ± 010 on Air corrector will be on the dyno anyway

 

[2002#3]

Gaps and distances between entries do not mean anything.  I (1) put spaces between ranges to make each range easy to discern and (2) to some extent, grouped similar ranges together.  Consider each entry an autonomous suggestion from one contributor.

Larry

[M3M3]

not intending to sound political, but had to say that given the current election...

 

no need for opinions, stick to the science.   ???    it makes no difference if it is stock carb, PPH, DCOE, or fuel injection.  the optimum ratios are the same.  this data can easily be found from many sources.

AFR Values & Characteristics in Four Stroke Engines
 6.0 AFR - Rich Burn Limit (engine fully warm)
 9.0 AFR - Black Smoke / Low Power
11.5 AFR - Best Rich Torque at Wide Open Throttle
12.2 AFR - Safe Best Power at Wide Open Throttle
13.3 AFR - Lean Best Torque
14.6 AFR - Stoichiometric AFR (Stoich)
15.5 AFR - Lean Cruise
16.5 AFR - Usual Best Economy
18.0 AFR - Carbureted Lean Burn Limit
22.0+ AFR - EEC / EFI Lean Burn Limit

 

downside of carbs is that you can't optimize for everything.  pick how you drive the car and try and get in the right time zone.  carbs are just barely controlled fuel leaks anyway..?

 

 

Edited October 13, 2020 by M2M3

[man_mark_7]

1 hour ago, 2002#3 said:

Gaps and distances between entries do not mean anything.  I (1) put spaces between ranges to make each range easy to discern and (2) to some extent, grouped similar ranges together.  Consider each entry an autonomous suggestion from one contributor.

Larry

Ah - got it. I was trying to read it as each row was one contributor. It should have dawned on me that there weren't 44 rows. Thx.

[TobyB]

BMW themselves say that best power is had at a lambda of .90- .95, and I haven't found that

the M10 is any different to any other BMW engine in that regard.

 

As with everything else, there are several factors that come into leaner burns,

most critically, timing- a lean mixture takes more time to burn,  so when leaning

out for light cruise, lots of advance makes lots of power from little fuel.

 

I agree with Marshall- our 'pinions not matter so much, as infernal combustion engines are

pretty well documented...

 

t

does like a good dyno now and then

[GazM3]

I’ve just been playing with the jets past few days after been pretty rich for quite some time.  
I ended up with pretty similar numbers.

idle: low 13’s

part throttle: mid 13’s

full throttle after 4000rpm 12.7

 

car really screams now to the low 7000’s and copes up hills in top gear with as little as 1500rpm on board.