Sorry if this gets a bit long�I would like to pass on the results of tuning the two Carter AFB carburetors on my 426 Hemi engine with the aid of an O2 meter. This is what I have, 68 Road Runner with 727 transmission and 4:10 dana rear. The engine is pretty much stock, factory intake, factory exhaust manifolds w/heat riser tubes and functioning choke, stock 68 mechanical cam. Factory dual point distributor with shorter slots and lighter springs. Repro exhaust from Accurate. Carbs were restored by Scott. First off, I can�t say enough good things about the great work Scott did on reconditioning my carbs. Knowing everything else was good on them made jet and rod changes easier without having to worry about something else on the carbs not being right. When I initially fired up the motor I had set my carbs up to run a bit richer than the factory jetting. I did the math and computed the area of the jet vs. area of the metering rod and set things up about 5-7% richer to compensate for today�s gas with ethanol blends. I got the motor running and even though it seemed to run well it still smelled a bit rich standing behind the car. I then had a few fuel related problems that I initially thought were caused by the carbs being lean � surging at cruise, etc. Turned out those were problems with the mechanical fuel pump and a loose clamp letting in air. So once those were fixed the carbs were even more rich. A buddy of mine has a LM1 O2 meter and offered to check my carbs if I would weld in the bungs needed for the sensor. I did that and then returned the jetting in my carbs back to 68 stock settings to establish a baseline. So Factory front carb setting was .089� primary, .080� secondary, .069�/.059 metering rods. Rear carb was .089� primaries, .092(left) secondary and .077� (right) secondary .069�/.054�left metering rod and .0715�/.058�right metering rod. Our local 93 octane premium (Exxon) has �up to 10% ethanol� so no idea really how much exactly is used. I also live 20 miles from the Ocean in Virginia so my altitude here is all of +20 feet. Driving out to my buddy�s place told me the factory settings were lean for cruise as the car had a noticeable surge, and the O2 readings confirmed this as well. It also told us that the Wide Open Throttle was rich. We made a few more changes to the metering rods, mostly in the rear carb, as we dialed in better numbers on the O2 sensor. I also noticed the car was responding as well with no more surge, cleaner looking exhaust tips and no more tears standing behind the car. This last weekend we made final metering rod changes and also to the secondary jetting to lean out the WOT numbers. I am going to call it good for now as I realize the jetting for carburetors, especially 2 of them, is all about compromise. I have cruise numbers in the 14.5 area and WOT runs in the 12.5 area with no pinging. Thanks to the guys in the other O2 tuning thread as I learned quite a bit from them. They are tuning at a level way above me but still a lot of good info there. So the final jetting numbers are not too drastically different but the O2 data backs up the changes. Hopefully it can be useful information for any other hemi guys running mostly factory configurations.
Modified front carb setting now .089� primaries, .077� secondaries, .069�/.059� metering rods. Rear carb now .089� primaries, .089(left) secondary and .074� (right) secondary .065�/.052�left metering rod and .067�/.055�right metering rod.
I�m sure I could get similar readings with different combos of jets and metering rods but my disclaimer would be that �It worked for me and your results may vary��

14.5 for cruising is a little lean, I would shoot more for 13.8-14.0...

And when you transition from idle or cruise to WOT it doesn't go way lean does it?

I did the driving and my buddy held the meter so I can't report the exact numbers of each transition. We did not have it set up to record to a laptop. He told me he could see the extra gas when we normally accelerated and stabbing it for WOT. We had to let that settle out briefly to get the WOT numbers.

Jim

I have my hemi tuned for about 13.3-13.6 at cruize though the numbers move with any movment of the throttle, and about 12.4-12.8 at wot. Car seems to love these settings. I have a a/f meter next to the water and oil gauges and was probably the one of the best things I did to the car. You have to be carful running to lean with a hemi engine as I hurt one. FHO who built my motor advised me what numbers to look for and said 14.0+ is to lean for his liking at cruise. At idle my car will go as high as 15.0+ at times you need to be carful when the engine is under a load as to what it is doing.

i used my meter and got my numbers looking good, in the ranges people talk about here. but it had a hesitation when giving it throttle at most positions, so i went one step richer on cruise and power, (it was the only metering rod i had that went one richer on cruise, and was close to what i had at power).

the hesitation is mostly gone now. comes up once in a while.

short story is that each engine likes what it likes, even if it differs from the norm.

Thats interesting. I never had any hesitation issues, just the surge. Both of my accel pumps are set for the arm in middle hole.

Jim

That's good info, I'm surprised it didn't want more jet. Lots of differences in fuel from place to place I guess.

Sheldon

First off that is a great looking RR you have there, you most be proud of it.
What heat range plug are you using?

What is the theory/thinking behind the right and left differences in rear carb jets/rods?

What changes cleaned up the stinky idle?

Hi.whath a f number do Yours hemi run,idle cruise wot

Anyone shed any light on this comment????

The factory OEM in line dual quad intake with the rear carb. being the part throttle running carb. dictates the overall jetting at WOT, the runner lengths on those intake are horrible once you take a hard look at them. I raced and tuned two different street Hemi cars(one stick and one automatic) in NHRA stock for several years, the jetting with open headers needs to be a little richer than stock for best MPH. Not much, maybe one Carter jet size depending on the D/A that day and track elevation, but a little. On the street with todays fuel a wide ban meter with recording capabilitys is your best tuning aid in my opinion. IHTHs