Can you run a Model A too lean?

[29 Tudor]

My A runs good with the GAV about 1/4 turn open after warming up. Just pulled to plugs for a routine check and they are all WHITE! Last time I looked at them, I had been running with the GAV at about 1/2 turn out and the plugs were a very nice light tan. I leaned it down a bit to see how it responded and while I don't think it has QUITE the power it did at 1/2 turn, it runs well. I have a feeling I'm running it a bit too lean.

Any thoughts or comments?

Thanks,

Steve