Carb tuning with wideband gauge

[Tdubbyount]

For those of you who haven't seen this or tried it for yourself, i wanted to share my experience and experimentation. I did a lot of research before buying a kit and figured it would be the best option for tuning my new carb to its full potential. I went with AEM's digital UEGO gauge kit. As far as quality goes, I don't see how it could get any better. It comes with a Bosch UEGO (universal exhaust gas oxygen) O2 sensor, so no worries there. The gauge itself comes with black and silver bezels and both black and white faces, so you can mix and match however you want. The LED display is bright and very easy to read. And best of all, its super easy to wire in. They've already done most of the wiring for you, all you gotta do is give it power and ground, weld up the bung for your O2 sensor and turn the key. They give you plenty of wire, so it will fit almost any application.

I put this in my truck when I built the new motor, so it really was a useful tool to get it running smoothly right off the get go. No guess work needed with this thing. The engine I'm working with here is a fresh 355, mild cam, hydraulic lifter, topped by a brand new out of the box Quickfuel Black Diamond 600cfm vacuum secondary carb. I started simply by setting idle, timing, air/fuel screws to where my vac at about 20 in. at about 1500 rpm. Then i paid attention to the wideband. I had no experience with these, but its pretty self explanatory. And its really interesting to put numbers to something I've always done by sight smell and sound. What i thought was somewhat "tuned in" was actually a little off. I was running pretty rich. Around 11:1 according to the gauge. As I'm sure most of you know, fuel injected engines always run at about 14.7:1. This is because gasoline takes approximately 14.64 or so lbs of air to completely burn 1 lb of fuel, leaving no extra. You don't want to shoot for this number at idle with a carb'd engine, because once you start driving, there's no computer to richen up your mixture, so you will run very lean during regular driving. Its also ok to run a little lean up on the top end with a carb'd motor. Most of them can take it, and you're not running high R's all the time, so it will do no harm. That's where you'll find the top end power anyway. You're shooting for a good balance. Not too rich, not too lean at part throttle. That's where your engine is going to spend most of its running time. Part throttle.

So after tinkering for a while, i went for a drive, and came up with some more results. At part throttle, i was running only 11-12:1. After a more extensive break in, I was comfortable to do a little WOT tuning. With a few hours and many "short drives" later, I got it to the point where I'm slightly rich at idle (about 12.5:1), anywhere from 13-14.5:1 at part throttle both town driving and highway, and only going slightly lean at WOT (from 14.5-15.5:1). I have to say, my truck has never ran this good! A simple little gauge has turned a total carburetor newbie into a half way decent tuner

I'd say this thing is worth every dime. It lets you really keep an eye on things and lets you get closer to that lean end of the spectrum where you're going to run the best, while still being on the safe side. And like I said, its really interesting to put numbers to something like this. So, fire away with any questions, comments, or suggestions!

[Jabes1]

12.5:1 is good for WFO. When I was running a Carter AFB I was as lean as 16:1 during cruise with no bucking or poping through the exhaust (automatic trans). I like Carters/Edelbrocks because they are super simple with Widebands because of the metering rods/springs. I always tuned for the most vacuum at idle via idle enrichment screws and it was pretty close to stoich when jetted properly. Being able to lean it out at cruise and throwing a bunch of timing at it on low load cruise is what will net you mpg. Widebands are a great tool in getting your ride to run crisp and tuned perfectly. Try jetting down your primaries to get it leaner at idle. Your pump shot should be adjustable that's what enriches and allows you to accelerate although Holley based carbs such as your are different I believe. With the Carter, I changed the squirters and adjusted the pump shot, don't always focus on the numbers because each engine is different with its needs, but do follow them as guidline and then jet the secondaries up or down to what you desire. Good job... keep on trucking!

[INSIDIOUS '86]

Open your pvcr's a little more if you want for about 13:1 wot mixture. But yes I'm planning to do this for mine sometime. Saves a lot of fuel for tuning since you can spend all day failing in a carb at a track.

Don't tune for numbers tune for what the engine tells you. You can prob get 15-17:1 ratio at cruise if the timing is good and an efficiant combustion chamber. Usually if its to lean you get surging. Any time you change timing you will change combustion characteristics and hence fuel needs so the car will have to be re calibrated.

[Jabes1]

I highly suggest the Chevy Talk forums, Innovates website along with a lot of reading... there tends to be a lot of misinformation based on opinions here, not actual real world experiences. Fueling a vehicle is the same whether its EFI or Carb'd, they are just tuned differently, but do the same things. An efficient chamber requires less timing than an inefficient chamber. Lean mixtures require the fuel to be lit earlier... its really all elementary and textbook. I went from carbs to EFI and I see numbers and correlations now. For example, during cruise on my EFI mill, I've grossly advanced the timing during cruise and my pulse width went down, meaning I'm using less fuel. Read... seriously, you will learn so much.

[gramps77]

Ive got the exact same gauge on my 65 Nova with a 355 and Edelbrock 410 hp topend. 670 Holley street avenger and found I was REAL close when I took it to the dyno.
13.7-14.2 at idle
14.7-15.2 at cruise
12.5-13.0 at WOT
you can see right when my power valve opens cause itll dump right down to almost 10:1 before it stabilizes

[Tdubbyount]

Thanks guys for all the input. I'm pretty new at this, and new at carb tuning in general. The more I read, the more I keep learning. There's just so much info out there! I'm gonna try jetting my primaries down a little and see if I can tame down my pump shot. Getting close though!

[SilverMiner]

Sorry to drag this semi-old thread back up, but I was wondering on which side of a true dual exhaust system should the O2 sensor be plugged into? Does it even matter? I haven't been able to find an answer to this either here or on other sites, so I'm starting to suspect it makes little difference unless there was something wrong with the carb/manifold/engine.

I'm about to pull the trigger and order from Summit what I think is the same AEM kit as Tdubbyount used. I'll be installing it into a basically all original 1980 K10 Suburban with an non-rebuilt original 70K mile 350, TH350 auto, 3.73 gears. I'm in the process of rebuilding the original Qjet using a Cliff Ruggles kit along with his book. I'd like to nail the tuning and see what this old engine can do when everything is working as it should. The exhaust is about one year old and is a true dual system off the original manifolds with no crossover or h-pipe going into Flowmaster mufflers. I'm toying with the idea of having my muffler shop install bungs on both sides and just plug them off until the AEM kit shows up.

[rich weyand]

That's a good question about which side of the duals to put the sensor on. I think it could matter with a dual-plane manifold, because you are basically running half the carb on each side of the engine, but only if you don't tune both sides the same. Same rods, same jets, same pump shot, same idle screw settings (# of turns out), then it shouldn't matter.

Pay attention to the numbers in the previous responses here. Idle around 13.5-14.0. Why? Because a carb doesn't give a uniform mixture at low air flows, and any cylinder that goes above 17:1 will not fire. At cruise, 14.5 to 15, to get your best mileage. Power circuit, back to 13.5. And at WOT, 12.5.