AFR readings not ideal?

So my set up seems to like a AFR reading at 11.0 at idle. runs great,plugs are 3 years old and show a greyish tan color. has a Lunati 703 cam and timming is 19 initial and comes in fast,total is 36*. all this on a warmed up 440. question is anyone else have a set up that seems to like a fat idle? maybe a novice question but the thought crossed my mind.

sounds like a legitemate question to me (I dont have an ans tho). I have yet to get my innovate LM1 hooked up.

That's a bit rich for idle, i assume that is fully warmed up?

When was the last time you calibrated the o2?

I agree but it runs good. when I lean it up to 12.5 it stumbles a bit off idle. car is not stinky but gas mileage is poor. running a 950 preform carb. I don't know anything about calibrating the co2?
I fully expect the poor gas mileage. maybe larger IFR's to lean it out? Forgive me I'm not worthy LOL.

any possibility there's a vac leak?

don't think so purs in gear at 700 rpm. idle screw adjustments are very responsive,1/8th turns makes a big difference. I'm thinking larger IFR's and maybe some larger squiters.? last time I checked vac was a steady 15.

How bumpy is the idle? The bumpier the idle, the wilder the idle ratios are likely to be. And the more lead the timing will want.

If there is much lope at idle, then I would shoot for more timing at idle. Something like 25* +/-. How did you arrive at 36* total as optimum on your combo? Low 30*s is more typical.

And unless you cruise on the idle circuit (which is possible) other circuits have a much larger impact on the cruise mix, which impacts the economy. Are you using the vacuum advance?

Are you adjusting for the best idle or are you adjusting to cover up the off idle stumble? Don't use the idle mixture screws to address an off idle stumble or hesitation.

I would adjust for the best idle you can get, don't worry about the A/F, and if the mix screws are in the 1 1/2 turn range, then you probably don't need to mess with the orifices or bleeds.

If you want it leaner, you want a smaller IFR, or a bigger IAB. A bigger IFR will make it richer.

Do whatever it takes to make it idle as clean and happy as possible and let the AFR land where it lands. Getting the transitions, cruise and WOT right is where your time is better spent.

I'd do a free air recalibration of the O2 sensor after double checking that it is wired EXACTLY as instructed. Wiring power and grounds other than what is instructed can cause a condition called ground differential which long story short can cause the instrument to lie to you. If the O2 sensor has ever been exposed to leaded race fuel it could be FUBAR also. Lead and O2 sensors do not play well together.

The calibration procedure should be in the installation instructions which you can usually download from the Mfg'r if you don't have them. Basically you take the sensor out of the pipe and expose it to the air and have the unit run it per the calibration instructions.

Kevin

What brand O2 system and where did you locate the sensor?
My pump gas car liked 14.3 AFR or leaner at idle warmed up to 160F+, it drove well with 14.3 to 15.3 AFR at light part throttle cruise up to 2300 RPM
I did have it below 12.8 AFR at idle and part throttle cruise and it blacked out and fouled the plugs
That was on pump gas with 91 octane, 518 C.I. low deck stroker motor with 440 six pack carbs on a low deck Eddy 383 OEM style six pack intake manifold.
I have learned to use my tuning tools to make me happy and not always use what is in print somewhere I don't know about and or trust
The spark plugs and time slip are good measuring tools

it idles smooth @ 700 rpm. 36* is just what it ended up at by trial and error. car runs good where it's at but off idle was just slightly blubbery off idle when the weather got warm. I do use the vac advance. I don't need to usemuch of the curb idle either but messing around with the carb I don't know how much of the t slots are exposed.

sounds like you are HAVING to run it rich at idle to cover up a lean tip in issue, may need a more aggressive accelerator pump cam, like the brown one,mine did,, lean it out at idle & try it, may need larger squirter.

The cam specs are 226/234 at 50 lift on a 110LSA. Idle should not be too lumpy, as indicated by the vacuum readings the OP is talking about.

Big block Mopars with original combustion chambers seem to like 38 degrees total mechanical advance. 36 is within the margin of error or the variability of engines.

In other words, I think you've found a good place for total advance.

R.

CO sensor?
Do you know anyone who has a CO sensor, possibly a small shop that used to do emissions testing?

I needed to get my truck emissions tested and the max allowable was 5%. The truck was much higher than that. At the time I thought it was clean because the exhaust didn't stink, but it was still way above 5%. I ended up testing three times before it passed. There WAS a noticeable effect on fuel economy, with it increasing as the CO numbers got smaller. Makes sense, right?
Carbon has to oxidize completely to CO2 to yield the maximum amount of energy.

R.

A lot off good points,Thanks! I'll play with the cams and see if I can clear up the lean tip in and lean up the Idle more. Also the o2 bung is welded into the collector on the left bank so could be sucking in o2 but I doubt it. Just needs more carb tuning. Runs well for the most part with no stink,fouled plugs but poor gas mileage . Just attempting to get it better then it is if I can.

If the O2 was getting air,it would indicate lean

True. Scratch that then.

Yes 11:1 at idle is a little rich for that cam and engine, especially if the compression is relatively decent.

That said.
If the fuel has less than 14.7 stoich, which is the case with most pump 'gas', then it will need to be richer than it would with a 14.7 stoich gasoline. If you're using race gas, look at the density and stoich data.

If no choke is used, then a bit richer mix idle all the time is often what works out as best. It may get warmed up enough to idle OK, but its not the same as a truly heat soaked engine.

The AFR gage may be fooled. Misfires, reversion and even the combustion process itself can cause the WBO2 or its interpretation to be off. Yes checking other gasses can help figure out what is really going on. There were good posts by Bruce 'Shrinker' Robertson at MSV, RFS and the ol Innovate forum on how WBO2 can be misleading.

I adjusted the carb to where I get a consistent 15.0 ish reading and same idle speed as before full warmed up and about the same drive ability but the idle is a lot choppier. I always thought you tuned for a smooth idle and more vac?

that would be my thinking/goal.

Its OK for stock and can be part of the strategy for modified as long as you understand the limitations.
a. The timing has to be established.
The reason for this is that continuing to advance the timing will continue to increase the manifold vacuum and also allow leaner mixture In Neutral. When put in gear, engine rpm (and vacuum) will drop bunch. This is because it is too lean to make power at idle.

b. The relation of the throttle blade to transfer slot has to be within working range. Old school Holley was .020 to .040 visible. Newer carbs sometimes have longer or wider slots but somewhere around square is a starting point.
Tip. When the carb is off; note the number of turns of the idle speed screw from just touching to .020, 030 and .040" inches. Write this in your notebook.

IF the transfer slot relationship is correct, then gentle acceleration from idle to off-idle will gently accelerate the car. If it gets blubbery or it hesitates and then goes, then some adjustment is needed in the idle circuit only after some trials to be sure the transfer slot relationship and timing can't be used to fix the situation.

And to compound the issue it's an auto with a fairly tight converter so the rpm difference between park and gear has to be close

Doesn't the cam have a lot to do with the idle steadiness and sounds

you dont have to shoot for 15-1,try 14-1 & drive it,see how it does.

The thing is the plugs look fairly clean, so I don't fully believe the AFR at idle has been 11:1 for the past 3 years.
Tune for driveabilty, efficiency and power. To rephrase another persons post, use the AFR numbers as a tool rather than target. As the car is an automagic, the vac reading in gear can also be used as another tool.

Typical 4stroke piston engines will idle (hot) most efficiently from 13 to 14, but can be a little higher or lower. An engine with a hot cam has overlap at idle that reduces combustion temperatures and also generally has lots of exhaust dilution. Because of these factors they tend to need more fuel to air than a combustion event with higher compression and less exhaust.

These AFRs are from the graphs in AFR Ratio Studies. See the fig 12 from Larew and 5-8 from Taylor along with Tuner's comments on hot rodded engines.

This thread may also be of interest:
Combustion Products post

Yeah I'll find a happy spot just posting for other opinions. I went around and around with the carb and timing for a long time last year and now decided to improve it because of the gas Mileage .

He said when was the last time you calibrated the 02 not the C02. Ron

Heh. I didn't read that carefully either.
a. Thought was looking for a CO2 meter ...
b. A Proform carb means that its likely the transfer slot is long or wide, the idle feed restricion is above fuel level and there's an extra 'emulsion hole'. (There have been enough of Proforms measured and posted on RFS forum to expect this is so).
Therefore establishing the correct transfer slot relationship may be more difficult. To go further in improving the carb performance, especially the "idle circuit", will require measuring and fixing these things. Once the restrictions and bleeds get outside of a certain range the fluid dynamics become erratic and less consistant. The "idle circuit" has a big influence on fuel milage especially below 55- 65 mph....