Hi Phil,
There's plenty of good advice already given so I can't add very much other than I'm also in the UK and so using the same pump petrol that you are. As John says, check the easy bits before diving into the carbs themselves, at least the ignition set-up and air filter before twiddling with the idle screws.
I changed to a hotter plug a few years ago on both the Elan & Europa because I only drive on the road and there's not many places around here where you can blast along for more than a few minutes without attracting attention. So the hotter plug works for me. I also have Pertronix electronic ignition & maybe that's helping as well.
I do use a colortune but as Rod says, they are mainly about setting the idle mixture. It's easy to see the flame and adjust the mixtures on the TC in a garage, not so much if you're using it outside in daylight. The downside is that if you've only one colortune then it's a slow process, one choke at a time but they do work pretty well - twiddle the screw, watch the flame change colour - low tech stuff.
The best book I've seen on the Dellorto carbs is Des Hammil's book "How to Build & Power Tune Weber & Dellorto Carburettors". It's generic of course but some very good diagrams, photographs and explanations of what goes on inside them. Miles Wilkin's book touches on carburetion in relation to the TC but I think Hammil explains the importance of float heights, accelerator pump jets and how they work much better.
The Yahoo group mentioned is excellent & I'm also a lurker on there, but the talk is mainly about webers and although they look similar there are differences in the way they operate so you might find some confusion if you're new to these carbs.
Brian
