Hi,
Advance springs are located in the cam sprocket, inside the head.
You are not able to see the springs directly, but you can easily confirm if these little parts are ok.
Use a timing light, and check with a running engine, especially between 1000 to 4000 rpm, and see if it's working to spec.
Jensen
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1965 Honda CP77 — Ulsan Metro City, Rep. Korea
Restored with original parts — Owner: J. Doe