AFR, what is your engine idle happy at?

[Scooter]

So I installed an AFR reader last weekend and started an embarrassingly stupid thread which I hastily deleted after reading more on how AFR works... so second shot at this.

Basic motor specs... "75" 360.. 30 over with a mild cam (Comp 20-212-2), steel heads with hardened exhaust seats, Weiand action plus intake with Holley Demon 625CFM vac secondary carb. TTI Shorty headers. Car is an automatic, factory stall. Timing 14 initial and 35 all in pretty fast.

Car was running fat as heck, like 10:1 AFR idle and 11:1 out and about. Eyes watering in garage fat.

Bought a calibration kit for the carb and after trial and error swapping out metering rods and springs I've got her running a lot leaner 13.5:1 at highway speeds and WOT. See a low 14 pop for a second or so occasionally on highway. I prefer to let her run a lil on the rich side than risk damage by being too lean.

The only "issue" I've really got left is setting the curb idle.

I use a vacuum gauge and the engine will pull nearly 18 inches @ about 800rpm, but the AFR is about 12.2:1. 

Seems a hair rich to me.. but she likes it.

Leave it or lean it and settle to 15 inches of vacuum?

I'm not getting any notable hesitation off the line at either setting.

Engine runs a bit more lopey at idle if leaned down.

[DeathProofCuda]

Seems to me like you could go either way.  Personally, I'd probably opt for the leaner and lopier option.  15" is enough vacuum at idle.  On the other hand I also wouldn't be too concerned about running a little bit rich at idle either. 

[Brads70]

Having a quickfuel carb I can easily tune it to run at 14.5 or what ever but found it likes 13.5. I also found using different brand fuel makes a difference too. When I use Shell Premium 91 - no ethanol
I run at 13.3-13.5 when I use Sunoco Ultra 94 it runs leaner especially at idle . Runs 14.5-14.7 driving then at idle runs 15.7-16.1 but the seat of the pants feels like less power with Sunoco.  Mind you I tuned it to run on the Shell 91 so...?  I only have  5-6 inches vac at idle....
I really praise the quickfuel carb and how every orifice that flows air or fuel has a removable/adjustable jet/bleed screw . Best carb hands down I have ever owned.
Only bad side it they really took a jump in price. I paid 600 something 8 years ago or so?  If I had to do it now I'd spend a little more and go EFI.  They are going to price themselves into extinction if they are not careful IMO?
https://www.holley.com/products/fuel_systems/carburetors/quick_fuel/q-series/parts/Q-850-AN

[Scooter]

^^^ Running Chevron 91 in it.. whatever blend is the flavor of the month.

Think if I was seeing 15's & 16's I'd fatten her up a bit to be safe.

You are spot on about EFI & Carb pricing.

With the Holley in tank pump that does not require a fuel return line.. it's looking even better. 

[dodj]

My idle is running 13.5 -14.2
About 12 or so when accelerating
14 to 15.5 cruising at speed.

I agree with Brad re: quick fuel.  Awesome adjustability.  I paid under 600 several years ago for a black diamond street series 850.
With the price closing in on 1k, efi is the way I would go today if I needed a new carb.

[Fastmark]

Holley bought out Quickfuel, byt.

[GoodysGotaCuda]

I would shoot for a little higher AFR at idle and perhaps bump the timing to help adjust the idle speed.


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