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Discussion Starter #1 (Edited)
Hi BB,

I am running a pair of Italian 45DCOE9's on my hot little 2L and to aid in tuning I recently purchased an AEM "UEGO" lambda sensor setup which consists of a Air/Fuel ratio gauge with digital readout, a calibrated Oxygen sensor, and all the mounts/wiring/etc needed to hook it up. I had already welded a bung for an 02 sensor when I had first got my car running, so it was a fairly easy affair to get this thing up and reading. I choose to get this tuning aid to assist me with my limited Weber tuning experience.

Long ago I learned in school that the ideal air/fuel mixture is 14.7:1. Does this mean that my car will always run better at this ratio? I ask because I had to really alter my main jet size to even start getting close to this ratio. Above 3K RPM, running on my 155 main jets, I was getting a air/fuel ratio of about 10.0:1 (way rich)! I installed the smallest main jets I had in my box (135) and I am now getting an air/fuel ratio of about 12.5:1 and the car definitely pulls harder and cleaner. I have to place an order for even smaller jets to try and get me towards the 14.7 ratio but I am being cautious because I don't want to blow up this engine with a overly lean mixture. I guess my question is: SHALL I CONTINUE TO GO LEAN? I am running RJ cams, 85mm pistons, Sperry stage 5 head with big valves, etc. I thought I'd have a thirstier engine than this!

All the above is in regards to the MAIN circuit, but my car is also running quite rich on the idle circuits. I have a pretty good selection of idle jets and was able to go from a 60F8 to a 50F8, however unlike the main circuit which took well to the change from large-to-small jet, my engine did not like the leaner idle jet, it starting popping severely off idle, yet still reading quite rich on the Air/Fuel gauge......confused......should an engine always run better at 14.7 or do some engine just want a richer mixture?
 

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Generally, you will develop most power just as the engine goes to too lean and something burns up. Unfortunatly Webers cannot compensate by themselves for cool air or changing barometric pressures, thus most err on the rich side to avoid potential disaster.
With pure race engines running high compression and plenty of ignition advance, a change of track temperatures of 20 degrees F or even less can cause noticible changes, some not for the good. FI can compensate for climate changes, and with knock sensors, even fuel differences. Webers cannot.
Most of us that have ruined an engine with lean mixtures (as I have), apply caution working toward maximum power with lean mixtures.
Idle circuit mixture is a bit of a misnomer with Weber as vacuum pulls from the "idle" circuuit when running on the "high-speed" circuit. Thus the "idle" circuit will effect BOTH transition to high speed and, to a lesser degree high speed mixture.
With the idle circuit, you look for smooth transition to high speed, bith with gradual acceleration and stomping on it with the pump jets. I recently ran into lots of transition popping on a race 1600 with #35 pump jets. #40's and no other changes resolved the issue completely. I did not expect that!
Unfortunately mixture will change with vacuum and thus engine speeds, using Webers. A GOOD set up is usually a good compromise, rather than an exact Lambda readout.
The above is just my opinion from my experience. Others experiences may differ.
 

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I had several different sets of cams in my 2L motor and I hardly had to touch the Webers until I installed Richard's cams and then it took me a while to get them right. I had to go several sizes smaller in main jets to get the mixture right in the 4000 - 5000 range but then the top end was lean and it could not be corrected by smaller air jets. The solution was to change the emulsion tubes from F41 to F34. The idle circuit did not need changes once I had the mid and upper end fixed. These are 40DCOE116/117's with 34mm venturis.
 

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Richard Jemison
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Jetting

I was getting a air/fuel ratio of about 10.0:1 (way rich)! I installed the smallest main jets I had in my box (.135) and I am now getting an air/fuel ratio of about 12.5:1 and the car definitely pulls harder and cleaner. I have to place an order for even smaller jets to try and get me towards the 14.7 ratio but I am being cautious because I don't want to blow up this engine with a overly lean mixture. I guess my question is: SHALL I CONTINUE TO GO LEAN? I am running RJ cams, 85mm pistons, Sperry stage 5 head with big valves, etc. I thought I'd have a thirstier engine than this!
First! Forget 14 to 1 with carbs!
Don`t use less than a 130 main jet if you have to experiment.
.
These cams demand less fuel at all RPMs to produce the same HP as old lobe design cams, due to reduction in overlap, but the additional lift and duration above .040 will need adequate fueling. I would hesitate to go less than .135s jets in fact. Under no load you can get by with 13.5 to one but not under load. That is lean enough.
As to higher RPM mixtures what Air Correctors are you running? What Emulsion tubes? Going to a slightly larger AC will lean out higher RPMS. But that is when lean mixtures will damage the engine so keep AFR around 13 and no more than 13.5 at cruise.

As for idle jetting because of long runners you have to have a richer mixture to keep drivability on throttle openings under load. A larger accelerator jet may solve the dead spot issue but the popping is from incorrect mixtures. (what is AFR when that occurs?) You have to run the engine at steady rate during that point for the fuel in the runners from the accel jets to burn out.
I suspect you need a idle jet of .50/.55 for quantity but with and a smaller air correction bleed hole to keep fuel flow greater (F6 series)
Regardless of AFR you have to have good responce at low RPMs. You can adjust the idle air needle to lean out "constant idle) as long as the accel jets are adequate.
Look at your accelerator pump bypas jet in the bottom center of the bowl. What is it? If it has any bleed hole pull all 4 and solder up the bleed hole. That should resolve initial "dead spot on open throttle. If you see black smoke on throttle opening, drill out the soldered hole to 1/2 the original size. No point in buying lots of jets.

While tuning take time to run the engine at adequate RPMs to clean the fuel deposits from the O2 senson. They don`t like rich mixtures and will give false readings.
 

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Discussion Starter #5
Richard,

Thanks for the information, I will go investigate exactly what jets I'm running and post them up. I'd appreciate any input.

Thanks
 

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Vespam,

How are you liking that AEM "UEGO" lambda sensor setup now that you have had it for a bit?

I'm thinking about buying one to help in setting up a new engine with untested carbs.


...And aesthetically, where did you mount the display? I'm not excited about a digital read-out visible in the cabin.

Thanks,

Alex
 

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Vespam,

How are you liking that AEM "UEGO" lambda sensor setup now that you have had it for a bit?

I'm thinking about buying one to help in setting up a new engine with untested carbs.


...And aesthetically, where did you mount the display? I'm not excited about a digital read-out visible in the cabin.

Thanks,

Alex
I like the AEM system quite a bit. I posted a video of it on a GTV6 here: http://www.alfabb.com/bb/forums/carburetors-fuel-injection-air-intake/295505-new-black-box-control-l-jet-fuel.html

The system is well made, and easy to set up. It also has software for data logging, but it's not really needed on our cars.
 

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Be aware that a single O2 sensor installation is averaging the output for all four cylinders.

I've tested engines with one oxygen sensor for each cylinder plus one for the collector. A total of 10 for a V8. It was not unusual for the collector O2 to show conditions to be where we wanted them, and the individual cylinder sensors' showing as much as a two point difference. Don't go too lean.
 

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Thanks for the input guys. I still have to do a bit of research on the right one.

Alex
 

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Discussion Starter #10
Be aware that a single O2 sensor installation is averaging the output for all four cylinders.

I've tested engines with one oxygen sensor for each cylinder plus one for the collector. A total of 10 for a V8. It was not unusual for the collector O2 to show conditions to be where we wanted them, and the individual cylinder sensors' showing as much as a two point difference. Don't go too lean.
This was one of my concerns as well.

I'm not finding the AEM setup to be very useful, I get wildly oscillating readings even within a certain rpm/throttle position, I'm sure the AEM is doing it's job but I ended up using driveability/sound/feel as my main tuning aid.

I will post a picture of my mounting later, it's really just a temporary setup which I plan to remove after tuning.
 

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Discussion Starter #11 (Edited)
First! Forget 14 to 1 with carbs!
Don`t use less than a 130 main jet if you have to experiment.
.
These cams demand less fuel at all RPMs to produce the same HP as old lobe design cams, due to reduction in overlap, but the additional lift and duration above .040 will need adequate fueling. I would hesitate to go less than .135s jets in fact. Under no load you can get by with 13.5 to one but not under load. That is lean enough.
As to higher RPM mixtures what Air Correctors are you running? What Emulsion tubes? Going to a slightly larger AC will lean out higher RPMS. But that is when lean mixtures will damage the engine so keep AFR around 13 and no more than 13.5 at cruise.

As for idle jetting because of long runners you have to have a richer mixture to keep drivability on throttle openings under load. A larger accelerator jet may solve the dead spot issue but the popping is from incorrect mixtures. (what is AFR when that occurs?) You have to run the engine at steady rate during that point for the fuel in the runners from the accel jets to burn out.
I suspect you need a idle jet of .50/.55 for quantity but with and a smaller air correction bleed hole to keep fuel flow greater (F6 series)
Regardless of AFR you have to have good responce at low RPMs. You can adjust the idle air needle to lean out "constant idle) as long as the accel jets are adequate.
Look at your accelerator pump bypas jet in the bottom center of the bowl. What is it? If it has any bleed hole pull all 4 and solder up the bleed hole. That should resolve initial "dead spot on open throttle. If you see black smoke on throttle opening, drill out the soldered hole to 1/2 the original size. No point in buying lots of jets.

While tuning take time to run the engine at adequate RPMs to clean the fuel deposits from the O2 senson. They don`t like rich mixtures and will give false readings.
Richard, I was playing with jetting over the weekend and up until now I've been running a 135 main jet. I have not been getting the best gas mileage and for that matter the car really doesn't rev out as crisp as it should. For kicks I down sized my main jet to a 130 and went for a test drive. Whoa, it really woke the car up! I drove hard for a few minutes up and down my test road and came back in for a plug check, the plugs looked that nice caramel color that they should be. I guess this car just wants a 130 main...at least this weekend it did. I'm running NGK BP6ES gapped at .034 FYI. I recently switched to these from the B8ES I was running before. For even more kicks I dropped down to a 125 and went for a drive, the power increase was minimal if any and the plugs were closer to white so I went back to 130.

Also I switched to a 60F9 Idle jet and with the needles out 2 turns, the car accelerates better and the popping stopped compared to the 60F8 I was running before. Seems like going richer helped. I have some 65F9 jets on their way to me which I suspect will allow me to run the needles at 1-1/2 turns where I am told they should be.
 

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I'm happy you have now confirmed exactly what both Richard and I, and now Ed have learned over the years. Webers cannot give uniform mixtures throughout all vacuum and load ranges. Yes you can measure the changes (and get wildly fluctuating readings) but you cannot compensate for them over the engines total load and operating range. NOW, as richard said and I will second, be SURE not to go to lean on the high speed jetting! At high rpm Alfa engines will burn up something VERY quickly at 6500 - 7500 RPM. I have done this with my mouse engines, and Richard may have had it happen with his monster engines.
It WILL happen. As I said, any engine develops it's greatest power JUST as it goes to too lean. Modern fuel injection with detonation sensors and instantanious mixture compensation are one thing, while Webers are quite another.
There are 2 GOOD reasons to run a slightly rich idle mixture. #1, is it will cover transition issues to the high speed circuit, avoiding bog. Older Italian Webers have run rich idle circuits forever, and racers love them (I'm building a pair of vintage 45DCOE9's for Roman Tucker as I write this.), for ease of adjustment, and getting through the "bog" (low vacuum transition) with BIG chokes needed for high speed power.
#2 Remember, low speed jetting ADDS to high speed through transition into the main circuit. A rich low end fills in a bit of rich mixture to the high speed circuit, BUT not the other way around! If you are running as lean as you dare on the high speed, and then LEAN your idle circuit, you are in for trouble. Conversely, if you are close to too lean on the main, and RICHEN the idle, the main will richen VERY slightly. This does not work the other way around. The main circuit will not change idle mixture as there is inadequate vacuum. To many this is a confusing concept. Clearly Richard understands this from racing experience, and I ALWAYS run my idle mix a bit rich with Webers.
I'm pleased you technical investigations have confirmed what OLD Weber users have always known. Ed has confirmed "what to do" with emission Webers that function is a similar way but with a "cleaner" and leaner idle circuit.
Interesting isn't it?
From the combined experience of senior Weber users.
 

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And to further demonstrate the versatility of the DCOE, the high end can be richened up by using larger accelerator pump jets. On the surface, a larger pump jet will deliver the same amount of fuel over a shorter period of time. At high air speeds however, fuel is sucked through the pump jet circuit. So, larger jet = more fuel at high air speeds = richer mixture.
 

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Discussion Starter #14 (Edited)
I have not experimented with pump jets yet, I did however forget to mention that I'm running an F11 Emulsion tube, I switched from F9 this weekend.
 

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And to further demonstrate the versatility of the DCOE, the high end can be richened up by using larger accelerator pump jets. On the surface, a larger pump jet will deliver the same amount of fuel over a shorter period of time. At high air speeds however, fuel is sucked through the pump jet circuit. So, larger jet = more fuel at high air speeds = richer mixture.
I just re-read John Passini's books and he makes the very same point.
 

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#2 Remember, low speed jetting ADDS to high speed through transition into the main circuit. A rich low end fills in a bit of rich mixture to the high speed circuit, BUT not the other way around! If you are running as lean as you dare on the high speed, and then LEAN your idle circuit, you are in for trouble. Conversely, if you are close to too lean on the main, and RICHEN the idle, the main will richen VERY slightly. This does not work the other way around. The main circuit will not change idle mixture as there is inadequate vacuum. To many this is a confusing concept. Clearly Richard understands this from racing experience, and I ALWAYS run my idle mix a bit rich with Webers.
I'm pleased you technical investigations have confirmed what OLD Weber users have always known. Ed has confirmed "what to do" with emission Webers that function is a similar way but with a "cleaner" and leaner idle circuit.
I know that this thread is not about emissions Webers but if you have them and you are reading this you should be aware that the interplay between the idle and main circuits is the opposite of classic Webers. With emissions webers, for reasons that I can explain but not here, the idle circuit does not have an additive effect on the main circuit and changes to the main circuit do affect the idle circuit. The biggest surprise that I got during my recent dyno testing was seeing the idle circuit lean out a bit when I put in bigger air correctors. Who would have thunk that?
 

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For reference here's the relevant chart from the Bosch manual. Max power is produced at about 12.6:1, a bit far from stoich. That's one advantage to keeping the carbs slightly rich, the other two are that:

- The power curve is a lot flatter in the rich region, so variations in mixture have less of an effect on engine output, and

- It gives you a bigger safety margin in conditions where the mixture might otherwise go lean causing detonation or burned valves

The disadvantages are obviously fuel economy and emissions, but those weren't much of a concern when these cars were shipping with carbs.

EFI cars run at 14.7 for emissions reasons most of the time, but at full throttle are designed to go rich for the same three reasons above.
 

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Here is my recent dyno curve for my Spider. You can see that the torque curve held up well until the AFR dropped below 11. This supports Tom's message that there are several reasons to stay on the rich side of stoichometric.

We were adjusting the Webers to maximize the area under the torque and power curves rather than maximizing the peak numbers. We made less total power when we ran a bit leaner.
 

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Discussion Starter #20
Really interesting and information, it's mind blowing how tuneable these analog devices are capable of! I've been doing a lot of tuning on air cooled Porsche motors lately via AEM stand alone managment where afr is altered via a couple key strokes yet it only makes me appreciate webers more.

Can someone chime in on how spark plugs factor into afr? Like I mentioned I did this tuning with NGK BP6ES plugs, for the sake of trial and error I popped in a brand new set of B8ES (my previous plug choice) and didn't notice much of a difference as far a driveability during my test drive....though a plug check showed the b8es seemed to stay whiter than the bp6es.
 
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