Well, MrsB was out yesterday, so I wagged gardening duties and spent half an hour soldering together my Jaycar mixture display kit. Dead easy construction, with a dozen or so components, excluding the 10 LEDs for the readout. A good introduction for someone who's never built an electronics kit before and a piece of the proverbial to replicate from various circuit diagrams on the web should you have a little experience and a reasonable stash of electronic odds and sods. Only difficulty I encountered was that Jaycar had provided a 100 MegOhm resistor instead of a 1 MO one. However, given that it was simply to protect the chip from excessive currents from the oxygen sensor and given that there should be effectively no current from the oxygen sensor, making the exact value of the resistor unimportant as long as it's big, I bunged it in anyway, on the basis that it should be OK. Worst that was going to happen would be that I'd have to dig another resistor out of the bits box and stick it in instead. Oh yes, and the fact that my eyes ain't what they were and I was having to use a magnifying glass to read resistor colour codes. Not too much of a problem given that I was using a multimeter as a double check. Anyhow, with everything glued together, I hooked it up temporarily to the bike, with a power feed from the headlamp fuse, an earth under a sidepanel screw and the signal wire crimped to the O2 sensor I fitted in last week's thrilling installment. Ignition on, fire up and wait for the O2 sensor to get up to temperature. I'm using a cheapo single wire unit with no integral heating element so it takes a few minutes. Once things were nice and hot, the readings from the LEDs looked reasonably sensible. At idle, there's quite a bit of flicker up and down the display, but given a few revs I get a nice, steady green a bit to the rich side of centre. There's a variable resistor on the unit to get this central, which I'll tweak before I start looking for proper data points. I suspect that the flicker at idle is a result of being a four-stroke single. Fresh combustion gases are only in contact with the sensor for about half a crankshaft revolution or a quarter of the full cycle, leaving one and a half revs when there's goodness knows what in the downpipe, composed of old exhaust gas, fresh, unburned fuel and air from valve overlap and whatever might make its way up from the tailpipe in the time available. The latter two would give rise to a lean reading, and the idle flicker observed seemed to favour the lean end of the scale and seemed to coincide with firing frequency. With more cyclinders, I suspect the effect would be less pronounced. It certainly seems to go away with more revs. Anyhoo, that was as far as I got before having to hurriedly hide the evidence of non-domestic type activity. Next step is to put the meter in some sort of reasonably neat housing and wire a suitable connection plug into the bike's loom. Having done that, I can get mixture readings at various throttle settings and engine speeds. I'm looking at doing quarter, half, three-quarter and full throttle at 1000 rpm steps from 1000 to 8000 (or less if that's too scary). That'll give me 32 data points. Not exactly a comprehensive fuel map, but probably all that my simple Engineer's brain and my goldfish like attention span will be able to cope with. Having done so, I can start looking at the effects that various modifications make. The baseline mixture readings will then, hopefully, allow me to tweak things like jetting and needle position to return fuelling to something close to standard. You will note that I will not be looking for absolute readings (which you simply can't get, with any accuracy, from a $20 Ebay narrow-band oxygen sensor. The purpose of getting baseline readings is to allow me to then do a comparison after modification that will tell me if things are leaner, richer or the same as stock. Using the instrument as a comparator should be fairly accurate. That's the idea anyway. Once I've proved to myself that the O2 sensor method works, I'll feel in a better position to drop a few hundred bucks on a Megasquirt kit and the associated ironmongery to go to the next step.