Just revisiting this thread, I dunno if they work but maybe, if you are really tryna grab just a bit more fuel economy you could maybe (as a wild card) try a Hiclone. I first saw this product around fifteen years ago (I think it was the Melbourne motor show) but I have never seen it in use, or owned one.

It was around 25 bucks back then, but it seems the price has crept up heaps! (perhaps development to fit it to different carbies was expensive - to be fair, that seems potentially possible) From memory the efficiency improvements they claimed were between 5 and 10 percent, I wanted one heaps for my HJ wagon (then a 202), but alas, on a musicians wage, 25 bucks was better spent on food at the Melbourne markets. (Awh us Aussies do it hard hey? 15 Mangos for ten bucks...)

Anyway I reckon someone must have tried a Hiclone but it probably should have its own thread, so I'll start one. It may be a dud thread but maybe the thing actually works, I honestly dont know.