Those out there with carbs or infact fuel injection for that matter, how lean can you push a petrol engine before you get meltdown! What areas suffer the most from ultra lean running?

I'm thinkin about this modified mk4 i'm plannin on doin, it wud b less hassle if i built a rev happy 1600cvh for it on DCOE 40's but i'm also concerned about economy!

I read sumwhere that sumone built a weber cvh with a big valve ported head etc and ran it at 40mpg or summit during the fuel crisis! that sounds good to me!

Can you run a cooler thermostat? That would let you run leaner right? But ive heard that engines run more efficient the hotter they are!