Basic, Basic Question on A/F Ratio
Thread Starter
Bud2
Joined: Jul 2005
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From: Warrnambool Victoria
Basic, Basic Question on A/F Ratio
This is probably a very silly question but at the risk of self embarrassment here goes. If you made a graph of the A/F mixture (vertical) over time (horizontal) you should be plotting a line around the magical 14.7 at cruse. Here’s the question – if the line is say at 16.5 is that lean or rich?
Another stupid question, if the A/F mixture is 16.5 would you increase the main jets or decrease to move back down to the 14.7???
The last question. When you mash the fast pedal, how much should the acc. pump push you off your car’s normal A/F ratio?
Using a LM1 A/F data logger and ran into something that has me questioning what I THOUGHT was right.
I'm in Australia so I won't be able to shield off your barbs until tomorrow.
Thanks.
Bud.
Another stupid question, if the A/F mixture is 16.5 would you increase the main jets or decrease to move back down to the 14.7???
The last question. When you mash the fast pedal, how much should the acc. pump push you off your car’s normal A/F ratio?
Using a LM1 A/F data logger and ran into something that has me questioning what I THOUGHT was right.
I'm in Australia so I won't be able to shield off your barbs until tomorrow.
Thanks.
Bud.
Thread Starter
Bud2
Joined: Jul 2005
Posts: 1,237
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From: Warrnambool Victoria
Ok, thanks for the reply. Let me get this straight, the carb is getting too much fuel, so when you say 'lean' you are talking about the 'air'? Not enough oxygen getting into the mixture. And you squeeze down on the jets to restrict the fuel, thus getting the ratio back to the norm?
How does that work with the commonly referred to 'rich mixture' depositing carbon on your plugs. Wouldn't you want to go to smaller jets for that condition too?
I just can't seem to get my head around this A/F animal.
What about the effect of the acc. pump on the A/F curve?
Bud
How does that work with the commonly referred to 'rich mixture' depositing carbon on your plugs. Wouldn't you want to go to smaller jets for that condition too?
I just can't seem to get my head around this A/F animal.
What about the effect of the acc. pump on the A/F curve?
Bud
Melting Slicks
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From: Western Washington
The larger the number the leaner it is. You would increase the size of the jet so it would get more fuel to richen it up. You are talking about the fuel (when changing jets) not the air. When you are at wide open throttle (WOT) it should be around 12.5.
Here is a little info:http://forums.corvetteforum.com/c1-a...-2-reader.html
Here is a little info:http://forums.corvetteforum.com/c1-a...-2-reader.html
Last edited by narlee; Jan 10, 2013 at 12:38 PM.
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A/F ratio is how many parts of air to fuel. So 14.7:1 A/F ratio is 14.7 parts of air to one part fuel.
So the larger the number the leaner, more air, the mixture is.
To change the A/F ratio you either change the jets or the air bleeds.
Joe
So the larger the number the leaner, more air, the mixture is.
To change the A/F ratio you either change the jets or the air bleeds.
Joe
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Thread Starter
Bud2
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From: Warrnambool Victoria
So at least I'm not the only one not quite confident on this beast. First of all, the figure 16.5 was just plucked out of the air not actual on my car. It's just that when I saw my actual A/F ratio, I did in-deed have a high number. I tried to correct it by increasing the jet size. WRONG! So to 'richen' up the mixture I had to squeeze down the jets. So if that is the way it's worked, so be it. BUT then I was reading that for optimum power 12.2-5 is required. You need to richen up the mixture from the 14.7 by increasing the jet size. But to get to 12.2-5, I would have to go smaller....Something seems to be ***-backwards. Or at least the terms 'rich' and 'lean' may have two opposite meanings - depending on when it's used.
Take for example, if your goal was economy, you would want to lean the ratio a tad. Wouldn't you want to restrict the fuel and make sure all of it was burnt? To do that wouldn't you want to decrease the jet size?
I dunno, I'm still confused.
Bud.
Take for example, if your goal was economy, you would want to lean the ratio a tad. Wouldn't you want to restrict the fuel and make sure all of it was burnt? To do that wouldn't you want to decrease the jet size?
I dunno, I'm still confused.
Bud.
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I just put an A/F meter in my '67 Chevelle and its been REAL educational. The car was running pig rich at part throttle and I reduced primary jets (Holley 4150) and I prob would never have done it without the meter. Plugs were dark but not awful and hard to read anyway with unleaded gas. Car didn't stink and no sooty exhaust either.
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So at least I'm not the only one not quite confident on this beast. First of all, the figure 16.5 was just plucked out of the air not actual on my car. It's just that when I saw my actual A/F ratio, I did in-deed have a high number. I tried to correct it by increasing the jet size. WRONG! So to 'richen' up the mixture I had to squeeze down the jets. So if that is the way it's worked, so be it. BUT then I was reading that for optimum power 12.2-5 is required. You need to richen up the mixture from the 14.7 by increasing the jet size. But to get to 12.2-5, I would have to go smaller....Something seems to be ***-backwards. Or at least the terms 'rich' and 'lean' may have two opposite meanings - depending on when it's used.
Take for example, if your goal was economy, you would want to lean the ratio a tad. Wouldn't you want to restrict the fuel and make sure all of it was burnt? To do that wouldn't you want to decrease the jet size?
I dunno, I'm still confused.
Bud.
Take for example, if your goal was economy, you would want to lean the ratio a tad. Wouldn't you want to restrict the fuel and make sure all of it was burnt? To do that wouldn't you want to decrease the jet size?
I dunno, I'm still confused.
Bud.
Installing smaller jets would decrease fuel and lean the mixture.
Not sure what you were seeing when you decreased jets and seemingly richened mixture...but that's not how it works.
Are you sure there are no air leaks...like header leaks or anything? A slight leak *header tick* can drive an 02 sensor whacky.
A big nasty cam can give a false reading also.
JIM
Thread Starter
Bud2
Joined: Jul 2005
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From: Warrnambool Victoria
Jim, see that's what I'm talking about, 180 degree opinions. My head says you're spot on but my LM1 says different (as some other people say too). My numbers were above 14.7 so I bumped up the jets a couple sizes and then the LM1 told me I was WAY lean. Plugs were sooty too. So I went the other way and now it's back to 14s. It's like the graph in LogWorks (LM1 software) is upside down. Now the 14s should be fine for the highway but for the strip I thought I wanted to get down to 12.2-5. I'm gonna have to drop down another size to do that. But that just sounds like it's wrong. My head says I should be pushing a bit more fuel into it not ween it off.
Bud.
The cam is big enough but not over the top.
Bud.
The cam is big enough but not over the top.
Melting Slicks
Joined: Apr 2008
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From: Western Washington
Not sure what is up with your gauge but if you have a reading, say 15, and you put larger primary jets the number should get lower, down towards 14 something. When you get the cruise AFR to 14.7 then you change the secondary jets to get to about 12.5 afr at WOT.
Le Mans Master
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From: Folsom CA
"Plugs were sooty too" Lean plugs are white from lean heat, Rich plugs are sooty from not burning your entire mixture.
Jim is dead on and your readings need to be ignored or you have a carb malfunction. Good luck and your head is correct and your plugs are correct the gauge is not based on your reports here.
Last edited by Westlotorn; Jan 11, 2013 at 02:59 AM.
Pro
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Jim, see that's what I'm talking about, 180 degree opinions. My head says you're spot on but my LM1 says different (as some other people say too). My numbers were above 14.7 so I bumped up the jets a couple sizes and then the LM1 told me I was WAY lean. Plugs were sooty too. So I went the other way and now it's back to 14s. It's like the graph in LogWorks (LM1 software) is upside down. Now the 14s should be fine for the highway but for the strip I thought I wanted to get down to 12.2-5. I'm gonna have to drop down another size to do that. But that just sounds like it's wrong. My head says I should be pushing a bit more fuel into it not ween it off.
Bud.
The cam is big enough but not over the top.
Bud.
The cam is big enough but not over the top.
Safety Car
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From: Ocean Township NJ
An overly rich mixture that's causing a misfire will give a false lean reading. Misfire results in excess O2 molecules, which are what the sensor is tracking.
This in addition to "the usual suspects": leaks, needs calibration, located too close to the terminus of the exhaust pipe, yada yada yada.
BTW: Some instruments, like the Zeitronix, needs no calibration.
This in addition to "the usual suspects": leaks, needs calibration, located too close to the terminus of the exhaust pipe, yada yada yada.
BTW: Some instruments, like the Zeitronix, needs no calibration.
Thread Starter
Bud2
Joined: Jul 2005
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From: Warrnambool Victoria
It's been calibrated a number of times. No backfires. Only think I can think of is the software.
OH, I've got it! Of course!!! The LM1 is a yankee product and I live in AUSTRALIA! Everything has to be upside down. I am SO dumb.....
Bud.
OH, I've got it! Of course!!! The LM1 is a yankee product and I live in AUSTRALIA! Everything has to be upside down. I am SO dumb.....
Bud.
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