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!

 

Doesnt sound realistic.

 

You can go very lean on cruise, even to ~20:1 afr with a good combustion chamber (not cvh). It's not the most efficient way though. On a CVH I run ~15.5:1 on cruise.
The first things to suffer from running too lean on high loads would probably be exhaust valves and plugs.