I'm kind of new to marine engines so this is probably a dumb question, why don't marine engines have some kind of vacume advance on the distributer? is it all mechanical advance? does the amount of timing you start with have anything to do with top end or max RPM?
Vacuum advance was used on cars to help with mileage and emissions. The advance adds timing to a car under cruise conditions when there is a high vacuum signal. When under load the timing reverts back to whatever the distributor is set up for. So since jet boats are basically always under load, there's no reason or need for a vacuum set up. Most boat people will set their ign timing to be all in by say 2500 rpm. Some will do this by locking out the mechanical advance and dropping the dist in at 32*-36* on initial timing, while others may still use dist weights and springs to achieve total advance, but keeping initial timing more around 10* or so for easier start up. Hope this makes since. Greg