I want to know if installing a narrow band air/fuel ratio gauge is a good way to tune my carburetor, or should I spend some big bucks on getting a wideband setup. I know the guys running fuel injection like to do this but there is no computer controlling my car. Right now I don’t even have a O2 sensor welded in the car. So would a narrow band setup be ok for tuning the carburetor, jets and so forth?

 

A narrowband sensor doesn't really tell you anything meaningful for tuning the carb.

 

I got a stand alone aem setup off of ebay a couple years ago that seems to work well. I originally used it to tune my carbed motor with no computer stuff. Granted it was also a blowthrough setup, but still a carb. Narrow band is really only worth anything at idle if it's even worth anything at all. You want to see something around 14.7 at idle/verry little load, and more like 12.6-12.8 WOT provided you're not using a power adder.

 

Even at idle on an open loop system you generally have to be richer than stoich for it to be happy.

 

I do notice that too, mine likes to be more around low 14's rather than upper. Kinda depends on the size of the cam doesn't it? Just figured mine liked to be richer because of the big cam.

 

Wide band is the way to go.
I use this model of AEM gauge with great results. Managed to coax more than 20 mpg highway too.

http://www.aempower.com/ViewCategory.aspx?CategoryID=67

 

What does open loop mean?

 

Open loop has to do with fuel injection, not really anything you need to know about at least for now. Believe it has to do with if the computer is paying attention to the oxygen sensor data or not.

 

so from what im getting everyone agrees, from a tuning point, a narrowband o2 gauge is worthless. Would it help me at all in determine whether i made the right step up or down in primary/secondary jets?

And while i have u guys on here with all this good info, i took my first vac reading on my motor today and came up with 13-14 in/hg. My motor is a 383. 10:1 compression and an edelbrock 7102 cam. Ive got a holley 750 street HP carb on it right now with mechanical secondaries. Ive changed the primary jets down from a 75 to a 71 and left the secondary jets alone at 80. and it seams to run alot better at partial throttle, but still bogs when i hit it hard. My question is what do yall think i should change the power valve to. its where it came stock now at a 4.5.
Thanks!

 

Vac. seems fine. Does it bog as soon as you hit it WOT or just in general anytime you're WOT. If it's as soon as you hit it, that means accelerator pump adjustment. Other thing might be timing, are you positive it gets 34-36 degrees advance above say 2500rpm as that could help.

The power valve you'll notice more on mid throttle when it opens, but if you're WOT it is open.

 

It bogs at WOT for a split second as soon as i step on it, then it runs real hard with no other problems. Distributor is msd 8551 locked down at 35 degrees advance.

 

So it probably needs more accelerator pump. Options are: different plastic cam pieces that move the pumps, nozzle size of the squirters, or if still issues a 50cc accelerator pump but you probably wont get that far. I'd say cams first since they're probably cheapest, but I think a bigger nozzle will probably do more change if you have really small drill bits and the nerve to use them, or just get bigger ones.

When I had the carb on mine with the blower, I had to put 50cc pumps on the front and back to get it to launch right and not do like what you're having.

 

so if i were to bump up the nozzle size would i do the primary or secondary or both? It has .031 primary .028 secondary. What would u change to if u were doin it?

 

It has to do with carburetors too, when they're computer controlled.

 

Check into finding a professional to tune your carb. I found a guy here locally that charged $85/hr which included unlimited dyno pulls. We had it tuned within in an hr and half which included changing the plugs, jets and messing around with the timing. I'll never do major tuning on my carb again as long as that guy is around.

 

I assume this was on a chassis dyno?

 

"Open" or "closed" loop refers to control systems of any type, with regard to feedback to commands. "Open" means no feedback, "closed" means the input is adjusted based on the feedback.

A cruise control is a closed loop feedback system - the cruise alters the throttle position based on the vehicle speed being monitored. If you had a throttle lock, that would be open loop no feedback because the throttle position would be set in one spot and wouldn't change when you go up or down a hill, for example.

The basic carb is an open loop system - mixture is controlled based on input only; the mixture isn't altered based on exhaust or other actual mixture monitoring.

 

Yeah it was a chassis dyno.

 

If you understand and work within the limitations of a narrow band O2 you'll find it a valuable tool to help you tune.
It will not tell you the exact AFR at WOT but will warn you when you are near, or at or leaner than 14.7:1 while rejetting up/down for power.

You'll find it very useful for dialing in the idle, off idle, idle air bleeds part throttle cruise AFR, cruise/power circuit (power valve) transition and accelerator pumps.
Knowing if you are close to 14.7:1 or richer than or leaner than at any time is very usefull.
You do not nessessarily need the AFR gauge if you have a good volt/ohm meter. Get a 3 or 4 wire O2 sensor with the built in heater.

 

I think you just talked me into getting one

 

I use this (NGK) NTK 21006 4 wire O2 sensor.
I made up a wireing harness using 4 conductor automotive/trailer lighting wire and 4 conductor flat trailer plug. Wired in a 12v cigarette lighter plug to get power off the cig lighter.

Autometer #3375 AFR meter.

I can mount the meter on the dash (1bolt bracket) next to the tach above the steering column or bring it under the hood while tuning.

If the header or gasket leaks the meter will read wrong as all it senses is left over O2 in the exhaust. Ignition misfire shows as lean spikes/rapid meter flutter.

If you mount the gauge in a cluster, together with a tach and vacuum gauge, you can poor man "data log" while testing, using a video camera or digital camera with vid capability.
Now you can concentrate on driving with your eyes on the road.

 

i used a narrowband sensor when i swaped to a carb set up so i could see what was going on, its not dead on but it at least tells you if you leaning out or going rich and it does help you get pretty close to the right tune