Flutter below 2k rpm

Stock Orange spring. I can try a lighter spring.


With the ethanol in fuel now its hard to read plugs... they always look white.

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Judging buy you're pic's you are way too LEAN.
From what I can see of the ground strap the timing mark looks low(towards the threads) this I believe means you are running to much advance.
Research threads on reading timing marks on plugs.
How many miles on the plugs in your pic's?