Well, over the weekend, I finally got around to pulling the downpipe off the DR and brazing in a boss to take an O2 sensor as the first step in the almost certainly very long process of teaching myself about EFI. In spite of observing surgical standards of cleanliness, the use of a torch that could melt the Bismarck in a matter of seconds, flux suitable for joining dissimilar metals and numerous internet assurances that brazing stainless is a piece of the proverbial, it took me a couple of goes before I got the thing stuck well enough that it didn't shear off when I tried tightening the sensor. I'm still not 100% convinced it's good, but it doesn't leak and looks like it'll hold as long as I don't do anything silly like ever trying to get the sensor out again. I was careful to site it in a straight run of pipe so that if it does drop off, I can effect a good bodge repair with a couple of jubilee clips, a tin can and some putty. Rebrazing wouldn't take that long and, you never know, I might actually get it right next time :wink:. Anyway, my cheapo Ebay sensor is giving what a digital voltmeter tells me are sensible numbers, so it just remains to build the kit I've got for an LED readout and I should be able to start getting baseline readings for fuel mixtures at various speeds and loads. I'd post a pic, but even I'm embarrassed by how ugly the whole thing looks .