I'm just a newbie who's trying to get the mixture set right on my '87 420SEL. I'm trying to avoid buying a duty-cycle meter if possible.

The car was running a little too rich to pass the smog inspection, but it almost passed. Based on the numbers, the smog shop said they think I need a new cat converter.

Now I had heard that adjusting the mixture 1/4 to 1/2 of a turn was a big change. However, I've probably leaned my car out over a turn already. Each time I lean it out it seems to run better, and the hesitation on acceleration that I was experiencing went away.

My question is, should I keep on leaning it out, or not? I'm wondering if maybe I leaned it out some more, it might pass smog without having to buy a new cat. But if I get it too lean, will I burn a valve or something? Or will it become obvious that it's too lean because it will start to die at idle? How about if I lean it out until just before it starts to die at idle? Would that be too lean?

Thanks for your help.