Nitrous on a 340 100 shot

Trying to save fuel in high gear low rpm it was 11.7-12 ish..... it idles at 12.5-12.8 now that I pulled more timing out of the top but added 5 degrees on the bottom. Now I have it set to 16*-31* and I'll try that and see how it is wirh nitrous. While I was timing that in I idled it for 10 minutes ish and the plug looks a bit better.

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You are still pig rich at 12.5-12.8 afr at idle. You need to trim some fuel out of it. The extra idle timing will help with the leaner mixture. And your plugs will clean up. This is when you get in to carb tuning that isn’t just mixture screws and jets. You might need idle feed or transfer slot restrictions to get enough fuel out at idle and still have enough in cruise.