AFR numbers for Weber

[Moto Carlo]

I now have a AFR gauge installed. Yahoo! Via the various forums, I  am getting mixed messages as to  the numbers to shoot for.
The magic number that keeps coming up is 14.7 :1 . (I am assuming that is warm at idle) 
But others say that does not apply to older carburetor cars. Also seems there should be a range of numbers.

 at idle - cruising - and hot foot - 
With an ideal  range we could dial in the different jets, not simply the idle jet...

Just curious, anyone work anything out for this?

 

(Sorry if this is an old topic, but I could not find anything with a FAQ search. )

[uai]

there are thousands of threads on the internet.

But in short ~12.8 =max power
14.7 ideal mixture for no co
If you have a little more than 14.7 with no heavy load at cruising it's not bad as it saves fuel.

Heavy load / and /or high revs for long time with more than 15.5 is not recommended.

If you'd be able to stay  between 12.5 and 15.5 and you're around 13 on WOT you're fine

Edited May 15, 2020 by uai

[AustrianVespaGuy]

And all M10s I know like to idle pretty rich, like on the order of 13.0ish for smoothest idle.  Cruising more like stochiametric (14.5-15.0), and 12.5-13.0 WOT.

[ray_]

[Chris_B]

4 hours ago, Moto Carlo said:

I now have a AFR gauge installed. Yahoo! Via the various forums, I  am getting mixed messages as to  the numbers to shoot for.
The magic number that keeps coming up is 14.7 :1 . (I am assuming that is warm at idle) 
But others say that does not apply to older carburetor cars. Also seems there should be a range of numbers.

 at idle - cruising - and hot foot - 
With an ideal  range we could dial in the different jets, not simply the idle jet...

Just curious, anyone work anything out for this?

 

(Sorry if this is an old topic, but I could not find anything with a FAQ search. )

You are not likely to see 14.7:1 during normal operation. Shoot for 12.5-13 for idle mixture, and ideally 12.5:1 at WOT approach redline. Your AFR between idle and WOT will vary widely, but if you are in the 13-14:1 range, count yourself lucky. BTW, you didn't say what kind of carb(s) you are working with. 

[TobyB]

What everyone else said.

 

I kept finding WOT power as I went leaner than 13:1-  I chicken out at about 13.5, as I'd see evidence of detonation at about 13.8ish...

 

But yeah, at light throttle cruise, 15-18:1, as long as it drops richer when you roll into it....

 

....it's too lean if it stumbles on that transition.

 

t

 

[Son of Marty]

Here's what we know for sure 14.7 to 1 is the perfect ratio for a single cylinder test engine running gasoline with no additives at room temp. We can't really achieve any of this and that's why they call it tuning. Try to get your numbers as close to those above while making your car run the best over the whole range. 

[ray_]

2 minutes ago, Son of Marty said:

Here's what we know for sure 14.7 to 1 is the perfect ratio for a single cylinder test engine running gasoline with no additives at room temp. We can't really achieve any of this and that's why they call it tuning. Try to get your numbers as close to those above while making your car run the best over the whole range. 

without burning metal.

[2002Scoob]

13 hours ago, Moto Carlo said:

Sorry if this is an old topic, but I could not find anything with a FAQ search.

 

It's all good. It's an old topic, but a relevant one for allot of us. And allot of the good info is hidden deep in other threads, too, and can be tough to find.  

 

I personally enjoy seeing such posts come thru. Serves as a good reminder for guys like me who are at 'good enough' but don't drive their car often enough to have their own setups supremely optimally dialed-in. 

 

Reminds me I need to spend more time (and unfortunately more money) on those pricy little brass bits to try out some different arrangements. Eurocarb must love me... sigh. 

 

 

[Zorac]

53 minutes ago, 2002Scoob said:

Reminds me I need to spend more time (and unfortunately more money) on those pricy little brass bits to try out some different arrangements. Eurocarb must love me... sigh. 

 

 

haha, i feel your pain. and most of them never sit in the carb for more than 10 or 20km....

[2002Scoob]

28 minutes ago, Zorac said:

and most of them never sit in the carb for more than 10 or 20km....

Oh man... IF that.

 

Sometimes it's a case of just around the block, or halfway down the street till you get a lean-stumble on tip-in. 

 

I'm always in the situation of deciding 'this weekend looks nice' where I wanna drive the car and tinker, but it takes a week or more for parts to arrive, so I'll order the combo i've spend 2-3 hours researching online  that I'm confident should be the answer, and then one step further just in case it's not enough.

 

70 euro spent.. Jets arrive.

 

Neither work exactly the way I was hoping... and I just go back to my original setup. It's too bad that professional tuning of these things around here has become a lost/black art, and my most trusted guy with a dyno and 'supreme guru' status is 5 hours away in Bavaria. 

 

Now HE works magic... Which is kinda dumb of me.. 2 tanks of gas, a cheap hotel, 1 weekends worth of time, and 300 bucks of dyno and I'd be gold. But I can't plan that far ahead.  ?

[jimk]

9 hours ago, ray_ said:

without burning metal.

That S14 stock Motronic used 14.7:1 for all off idle loads except when the WOT switch was closed where it reverts to a WOT map and drops power to the narrowband O2 sensor.  It did not have the ability to do otherwise with the narrowband O2 sensor.  I examined the chip data when I was setting up my ignition advance table for the Haltech.

I realize you not have it tuned to other ratios, but the comment relates to the question of how was it that BMW felt 14.7:1 was ok for the cars as they left the factory.

Edited May 16, 2020 by jimk

[Moto Carlo]

Once again a gold mine of info. 
This is all pretty much concurs with what I have found at other sites.
14.7:1 is the ideal, but .. er... uh...

 

Sorry I should have mentioned the carb : Weber 45 dcoe  single side draft.

 

Thanks one and all.

 

[steve k.]

14.7 is a stoichiometric (stoich) at which both gasoline and oxygen are fully consumed during the chemical reaction. Other fuels will have different numbers. If your AFR is above 14.7, you are running lean (more oxygen then needed to complete fuel burn), if you are running bellow 14.7 then you are running rich (more fuel than needed)

 

General consensus is that you idle at stoich, cruise at slightly lean (up to 15.5), and max power at slightly rich (no less then 11.5)

The actual numbers will vary based on efficiency, timing, all sorts of other things. 

 

One thing to remember is that your AFR today will not be the same as your AFR tomorrow or even 2 minutes from now. Carburetors measure air by volume only, so the amount of oxygen in the air will always differ based on temperature and pressure.  EFI system will include at least and air temp sensor in addition to oxygen sensor to help ECU decide the volume of oxygen. Adjust your jets based on the type of driving that you do in the condition that you have. 

 

On the Autcross car I used to tune the carbs and later the EFI to run at full throttle. It is easier to tune EFI to be more efficient at different stages, with carbs you mostly aim at one spot and hope the rest follows. DCOE carbs give a little more adjustability than DGAS or DGAV, but at no point will you be perfect. 

 

If none of the above sticks  aim at this

 

WOT 11.5 - 13.5

cruise 14.7 - 15.5

idle 13.5 - 15

 

steve k.

[rcf925]

After spending hours and hours tuning my italian dual weber 45's I'm glad I did, Cured all my problems and learned a lot in the process, Latest was stumble under load in 4th and 5th gear at high revs, Thought was fuel pressure but I decided to check carb sync again and sure enough cured the problem, Not perfectly synced carbs cause all kinds of problems, Cured stumble off idle by going to 60 idle air jet from 50, Tried 65 but that was too much, Same with main jet started with 125 went to 130 then 135, Back to 130, Pulls hard all the way to 7500 . Last problem I'm tackling is my linkage which is IE early cable which is not very smooth or responsive so just ordered different style to smooth that out and I should be done.  Tried finding locally a weber guru at numerous local shops, Crickets, Nobody would touch them. So anybody contemplating going to dual set-up be prepared to do it all yourself.