Evan G Posted August 25, 2009 Report Share Posted August 25, 2009 my carby mixtures are up the shit so I'm thinking, getting a 3 wire O2 sensor and finding the manufactures valves for rich and lean (.1V lean/5V rich) hooking it up to a multimeter, montior the voltages while I'm adjusting the mixture screws untill i get to stoich sounds like something i can do and reltively cheap ideas? Quote Link to comment Share on other sites More sharing options...
Felix Posted August 25, 2009 Report Share Posted August 25, 2009 (edited) Get yourself one of These Get a M18x1.5mm nut and grind it to suit the outer curve of your exhaust. Drill exhaust, weld on nut, and screw in your O2 sensor. Make sure the O2 sensor is a heated type. Great for tuning carbs. You can easily dial in a weber in a few hours if you have a good selection of jets available. Oh yea the mixture screw is only good for setting the mixture at idle/progression. It doesn't have any affect on the mixtures once you get onto the main circuit. Edited August 25, 2009 by Felix Quote Link to comment Share on other sites More sharing options...
Evan G Posted August 25, 2009 Author Report Share Posted August 25, 2009 heated is a 3 wire Quote Link to comment Share on other sites More sharing options...
Felix Posted August 25, 2009 Report Share Posted August 25, 2009 Ahh ok. Wasn't sure. The one I put in my ke15 was a 4 wire type. Quote Link to comment Share on other sites More sharing options...
Evan G Posted August 25, 2009 Author Report Share Posted August 25, 2009 Three Wires - One wire carries the signal and two wires are used to supply a voltage to the internal heater. Signal ground return is achieved through the vehicle body. Also referred to as a HEGO Sensor (Heated Exhaust Gas Oxygen Sensor). Four Wires - One wire is the sensor signal, one is the isolated sensor signal ground and the remaining two are used to supply a voltage to the internal heater. Also referred to as an ISO - HEGO Sensor (Isolated Heated Exhaust Gas Oxygen Sensor). The sensor signal wire is directly connected to one of the platinum electrodes on the ceramic element. The sensor output is immune to ground loop voltages and also to large resistances in the vehicle ground return, caused by corroded connections. No NTK four wire sensor is case grounded. Case grounded sensors have the ground wire physically attached to the sensor body. It is not recommended to replace isolated ground sensors with case ground types. Quote Link to comment Share on other sites More sharing options...
Evan G Posted August 25, 2009 Author Report Share Posted August 25, 2009 (edited) wait so felix if have it running super lean/ rich at idle but through the rev range it will be normal AFR? Edited August 25, 2009 by Evan G Quote Link to comment Share on other sites More sharing options...
Felix Posted August 25, 2009 Report Share Posted August 25, 2009 wait so felix if have it running super lean/ rich at idle but through the rev range it will be normal AFR? Yup. It is called the Idle mixture screw for a reason. :P For some reason a lot of people seem to think it controls the mixture throughout the entire rev range... which it doesn't. Only idle and progression. Download and read this. It is a scan of the carb chapter from A. Graham Bells' book "Tuning New Generation Engines for Power and Economy". Quote Link to comment Share on other sites More sharing options...
irokin Posted August 25, 2009 Report Share Posted August 25, 2009 FWIW IMO narrowband O2 sensors (the vast majority of oxygen sensors) are pretty much useless for any type of tuning. They'll usually either show full rich or full lean and rarely anything meaningful in between. If you want meaningful numbers to tune by you'll have to fork out for a wideband sensor. Quote Link to comment Share on other sites More sharing options...
Evan G Posted August 25, 2009 Author Report Share Posted August 25, 2009 Yup. It is called the Idle mixture screw for a reason. :P For some reason a lot of people seem to think it controls the mixture throughout the entire rev range... which it doesn't. Only idle and progression. Download and read this. It is a scan of the carb chapter from A. Graham Bells' book "Tuning New Generation Engines for Power and Economy". thanks for that felix Quote Link to comment Share on other sites More sharing options...
Felix Posted August 25, 2009 Report Share Posted August 25, 2009 You'd be surprised Irokin. Carbs are an analogue device and hardly as precise as EFI. The Jaycar kit basically is like an expanded scale multimeter, it stretches out the readings between lean and rich. The numbers it gives may not be exact, but they are relative (carbs are not exact lol). You can immediately see the direction of jetting changes. As I said previously it makes setting up carbs a breeze. I wouldn't use one for tuning a highly strung turbo car, but for carbs they are great. Quote Link to comment Share on other sites More sharing options...
irokin Posted August 25, 2009 Report Share Posted August 25, 2009 I had one in my celica for a year or so and found it virtually useless. From a scientific point of view the resolution where it counts is too poor. These things were only designed to measure when an Efi computer had crossed stoich and to tell it to go back the other way. Rinse lather repeat. Stoich isn't even necessarily correct with these things either. With a resolution so poor the calibration for stoich cold be anywhere within a couple of volts. I just don't feel you can have enough confidence in what they're telling you to have meaningful results. In my opinion the only thing you can be confident of is full rich and full lean which, depending on the sensor, could be something like 10-17. A huge range! I don't doubt you have been able to tune cars with the assistance of a narrow band sensor, but you have skills in addition to a sensor to assist you. Many other people haven't learnt those necessary skills. A wideband for the most part would remove much of the need for those skills and pehaps assist in aquiring them. By all means Evan put one in and have a crack. It cost me maybe $30 to do. You might have success but bear in mind the intended use for these sensors and have a look at their calibration graphs. Quote Link to comment Share on other sites More sharing options...
Felix Posted August 26, 2009 Report Share Posted August 26, 2009 The Fuel mixture meter I linked to is a LOT better than the LED bar type, the number display has a lot more resolution than the cheaper more common bargraph type with 10 LEDs. For a few hours and $100 setup in the car including an O2 sensor (free) and welding at a muffler shop, it is a cheap tuning/diagnostic tool. Way better than stumbling in the dark. When you consider that the majority of guys on here consider tuning a carb to be just fiddling with the idle mixture screw, one of these things is a good investment. Coupled with a vacuum gauge, stopwatch, some carb jets and a measured approach to tuning the various circuits in a carb... anyone is capable of making a noticeable improvement to the fuel economy, drivability and outright power of their car. I've got this old school portable (yea right) combustion analyser and the readings between it and my O2/FMD meter were pretty much spot on across the board. :P Quote Link to comment Share on other sites More sharing options...
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