What manual are you using? 90-861326--1?
Ignition Timing Checking/Adjusting found on page 4B-13
Steps 3 and 8 seem to cover this pretty good.
3. Manually adjust the engine throttle to 1800 rpm +or- 200
8. Manually close throttle to bring engine down to idle state.
What is missing in this section (it's found in the fuel section) is that the engine may die when put in service mode, so you might need to advance the throttle before selecting service mode. ------- I find it kind of funny that now a day's you need to read 2 sections of the service manual just to check timing, and remember that you have what is almost the simplest EFI system out there.
Another thing that some people miss is that the procedure starts with.
The engine must be at NORMAL OPERATING TEMPERATURE for this adjustment.
MerCruiser puts it in capital letters, but I don't remember ever seeing anywhere in the manual the explanation that its very difficult to reach "NORMAL OPERATING TEMPERATURE" without a load on the engine. Some people think that when the thermostat has opened it has been reached. Nope it's once oil temp has stabilized and that's quite a while after the thermostat has opened. But I have found only a few times that it made much of a difference. Still I recommend that you recheck the timing once the boat is back in the water and run under load for 15 minutes. You may find that the throttle doesn't need to be advanced before selecting service mode and the timing has changed a degree or two.
I can't help with the jumping of terminals A+B because I have always used a scan tool for this job. But make sure your doing this at the DLC and not the distributor.
