So here is what Merc says:

Ignition Timing
EFI/MPI Models
1. Connect timing light to number 1 spark plug wire.
2. Start engine and run at 1300 rpm until it reaches normal operating temperature.
3. Stop engine and connect the scan tool or timing tool to the DLC connector on the wiring
harness.
4. Start engine, allow rpm to stablilize.
NOTE: ECM will automatically adjust engine rpm to approximately 1200 rpm when put in
the service mode on a scan tool or when using the timing tool.
5. Check igniton timing. If incorrect, rotate the distributor until timing is correct. Torque
clamping screw to 18 lb-ft (25 Nm).
6. Recheck ignition timing.
7. Disconnect scan tool or timing tool from DLC connector.
8. If required, return remote control throttle lever to idle position and shut off engine.
9. Restart engine, increase rpm to 1300 then return to idle position slowly. Ensure that
engine returns to idle rpm. Readjust throttle cable, if required.
10. Shut engine off.

What if you don't have a scan tool / timing tool handy?

Anyone? (Mobile Merc Man?)

Thanks,
Dave

Ttt???

Everybody Believes timing should be some set # Before TDC, When actually what you want is your Max Explosion to be between 15*-20* ATDC, this is where the crank journal goes from moving laterally across the bottom of the bore, to moving Down, if this is where your max cylinder pressure is, this is where your max power is. whats happening (happens Fast) is Before the piston gets to TDC, Light the Mixture and let it burn and try to get the Max cyl pressure right when the piston starts going back down the hole. Different fuels Dictate when the spark should start (Advance) and you should adjust yours accordingly you may have to move 2*,3*,4* in either direction but when you get the right spot you'll know.

So depending on your set up and what fuel you use determines what your best timing will be. Yes there is some # that fits everybody but is that the best # for you?? Probably not.....Test, Test, Test...