someone was telling me in order to set the timming on the Merc 575 Sci, you have to bypass or do something like that to the computer?

On the data link connector, jumper pins A and B together,

or ground pin B. Pin B should be a WHT/BLK wire, pin A is
a BLK wire (obviously pin A is ground).

The data link connector is the connector at the rear of the
engine for the diagnostics.

Pesky Varmint

Thanks, let me ask you another questions what will happen if I set the timming with out jumping the computer?

Merc makes a timing tool that is very cheap, that jumps the two pins. It comes with instructions. Basic timing is set at 8, at 1800 rpm.

If you try to set the timing without the jumper, the timing
won't be sitting still at any particular setting, it will be jumping
all around. The timing continually varies because it is partly
how they control the idle speed.

At least thats what the guys at Arizona Speed and Marine
told me.

Pesky Varmint