Mercury 18 Hp timing

[TheMadMariner]

Hey there chaps,
I think the Idle spark timing on my Mercury 18HP is off. It's out of the 18/20/25 hp series build from '84 to '87. It will idle very rough with the primer engaged, otherwise it will stall out..I know this won't be the entire problem, but I just want to rule this out.
However, this model doens't have a regular numeral marks on the flywheel, but has dots instead, I will include a photo very soon.


Anyone a guess how i'm supposed to read this?
Thanks a lot in advance!

[uncle al]

you could buy the factory issued service manual, if you do have the s/n handy in case its required then all will be explained, you will also need a timming light and a rev counter to do it properly, it reads hard but it is an easy job with the correct tools