Some of us on here lock our timing on the MSD distributors at the total advance. For the life of me I dont know why this works. When I first got my boat it was locked at 35 and it started like a champ. First rotation or two it would fire right off. Then I started playing with a new Carb, etc. , rebuilt the motor and put some intitial in and it wont start worth a darn. I think its a carb issue so this year I will get that nailed.
But for what its worth running with the timing locked worked for my jet boat. Some people run with ingnition switches. Get the motor turning over and then let it fire. I have heard that works as well.
Good luck,
RandyH