This doesn't quite stack up for me. If you are getting the correct flame colour throughout the rev range for standard engine, and not for a modified engine, that's because the modified engine has not had it's fueling set up correctly. Either needle is wrong, or spring, or something else. It's not the colortune giving a bung reading. Afterall it's not a 'reading', it's simply letting you see the flame front.

Now, getting a correct colour through the rev range IS a bit tricky with colortune, as if you just sit there revving the tits off it in the driveway you are getting high revs with no load, which is not what you'll get on the road. But it's not a modified versus standard tune thing. Funky article out there somewhere from Vizard (I think) about using a colortune as a rolling road dyno: basically jack the car up, and drive with your foot on the brakes to simulate real driving

_________________
http://www.mini-hb.co.nz

The context use of the colortune is for the tune to be set at idle and the remaining tune to follow through from that point. This is simply an optical method of the audible method described in the manual. The point of the gunson is lost if (as Vizard had to), you need to put the car up on blocks and have someone rev the engine and smoke the brakes with your head under the bonnet to watch the gunson. That's really not work for the average punter I think.The original context of Vizard was thirty years ago. O2 sensors were pretty well top end equipment only and he did what he had to do.

If you use the gunson at idle on a tuned engine, you will find it missing under load. So now you screw the mixture out a couple of turns to fix it, but now that you are guessing, the gunson could have just stayed in the drawer. Still, I love the colortune, and use it a lot but only on pretty mild engines.

There's better out there I am sure, but I have built up one of the tech Edge WB02 sensor kits. You only need to have an 02 sensor adaptor fitted to the header under the car. http://www.techedge.com.au/

_________________
SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.