You didn’t post your engine serial number so I can only offer general advice.
Ignition timing is NOT something you can adjust without reprogramming the ECM. Because it’s solely controlled by the ECM. Turning the distributor will NOT change the timing.
To check timing you will need a scan tool because that’s the only way you will know what the ECM is setting the timing at.
As someone who uses both of the scan tools
alldodge has recommended. I will offer my advice. The Techmate is best for the quick and easy jobs, the screen is easy to view it the sun. But requires that the person using it has full knowledge of how the engine system works (basically a fully trained tech) because you see everything in real time. So you need to know what you’re looking for and also what a normal engine should look like. The Diacom runs on a laptop so it is almost impossible to use while your driving the boat, but it will make recordings. So you can do a test run and then review it once you’re safely back at the dock. Diacom also allows you to see multiple parameters at once, which can be very important. Also allows you to slow down the data so you can see glitches that you wouldn’t be able to see with the Techmate.
Having both is nice, but if you only have one. It should be Diacom.
alldodge posted a link to the service bulletin that describes how to build the tool for setting the distributor on a MerCruiser. It is the best way, and it should be how your service provider did the job. If they didn’t, think about finding a new service provider.
