You'll need a timing light.

If you advance the timing too much in the base adjustment you'll be lighting the fuel when the fuel mixture is not compressed and you'll running out of spark at the higher rpms.

If you retard the initial adjustment you'll be firing the fuel mixture after the top dead center as the piston is on its way down.

Both overly advanced and overly retarted timing will cause a loss of power, incomplete combustion, higher emissions and poor fuel economy.

In short, don't monkey with the timing, bring it to the garage.