Inliners International Forums General Discussion Engines air/fuel mixture gauge

Has anyone installed an air/fuel gauge and oxygen sensor? If so would you tell us about it. Sensor type and location, gauge brand. Is this of any value with a carburated 250?
Thanks.
Ken

I use a hand held type from NAPA for tuning. Its a older model with a tail pipe sniffer. Its real handy when setting multiple carburetor idle screws. As far as a everyday gauge, I'am not sure you would get much out one, it might scare you to see how rich and lean they run at times! I set my mono-jets to idle and run in the fuel injection range, I figure if its good for my '03 Toyota, then its good enough for a '70 Chevrolet.

You can just install a 02 sensor and read it with a multi-meter, if you do a google search, there are a few sites that explain how to read the sensor. 02 sensors create there own signal so no power is needed for them, the multi-meter simply read what the sender is doing and you convert the readings to ratio's. I believe any 02 sensor will work and you want it in the hotest part of the exhaust stream, usally about 6 to 8" from the header outlet or exhaust manufold outlet

Joe

Expensive wideband unit's are good. The LED type are pretty useless for setting up a carbed car. They basicly read correct at 14.5 AFR and just tell you if you are over or under from there. I have an 30 year old tailpipe sniffer, and one by Inovate that works very well as a mobile unit if you have a bung for the wideband O2.

Gentlemen,
Thank you. I believe I'm running rich, but I have no way of telling. I set my idle mixture to produce the highest vacuum I can get, but that's the only tool I have. That's why I thought it might be useful to either install an O2 sensor and use a gauge, or find a device that I can "sniff" the tailpipe.

Ken

Ken

I believe I'm running rich

Why?

The inside of the tailpipe is always black even after a 50 mile at 65 mph cruise.

Ken

With the advent of lead-free gasoline and converters All tail pipes now run black. The old white or light gray tail pipe colors when run at highway speeds with light throttle settings were caused by the lead deposits from the old leaded gasolines.
Nowadays when you pull a head of an engine run with lead free gas for even 100,000 miles the chambers are unbelievablely clean and free of carbon deposits, it seems more like candle soot. This is why spark plugs seem to last forever (of course the tips are now tungstun and certainly help longivity)but even their coloring make them look nearly new. As a diehard presmog addict, I have to conceed to the presence of these visible effects of leaded gasoline (damn it!).

EDSKI,
Thanks for the info. I will no longer labor under the mistaken belief that I need to see white. That said, how do you measure your air/fuel mixture?
Respectfully,
Ken

I run an autometer guage with the o2 sensor abiut 6" from the manifold. You can't panic when it says rich or lean because moving the throttle pedal will change that. But as you drive it you can determine an average mixture under different conditions then rejet to suit your desires. Just a ten mile ride once won't tell you much, unless you are way off and are showing one extreme all the time.

Truthfully, you can get about as much information from seat of the pants if drive carefully. Just jet down a size or two and drive for a week. You will know pretty quickly if you went to far.

Idle adjustment only effect idle, once you open the throttle, the idle circuit closes. Adjust it lean, but not so much it won't idle under all driving conditions. In some cases if the carb is really lean, a rich idle adjustment can over come some of the stumble associated with a lean mixture.

Advancing the timing can do wonders for economy. Since we have better fuel now a days, you can run way more timing then the books say. I run mine up around 12 or 14 degrees, I believe the book calls for 8. It never pings since the compression is low, it helps the idle, and I run on the lean side. I still only get 14 or 15 mpg @ 70 mph due to the tall truck and terrible aerodynamics of a 1937 Chevy pickup, but at 45 to 50 mph the economy really jumps.

You can also fine tune the carb with different metering rod springs. A soft spring will hold the metering rod down (lean) longer. Vacuum operates the metering rod linkage, so the rod stays put with less vacuum if the spring is soft, a stiff spring over comes the vacuum quicker letting the fuel circuit go rich quicker.

Ideally you want to jet for full throttle so the engine runs its best, then fine tune the metering circuit for part throttle and cruise, and finally set the idle circuit for clean idle. Its not that easy, but you get the idea.

Joe

Joe

Gentlemen,
Thank you all for your help.

Ken