G'day Mate,
Yeah I know how to tune by ear,
that's why I gave the advise about raising the nose, you can hear it speed up, when it is rich enough.
& I think you will find that the OS #8 is not too cold, it is a medium plug, the A5 is the colder one. I don't like the OS A3, they are cheaper for a reason, they are plated plugs & don't last very long, compared to the #8, using around 10% nitro.