I am a big fan of KISS (keep it simple stupid), but the more I read about setting up timing on a marine distributor, the more I come across people who have had problems setting the timing for a good compromise between Idle and Loaded.

A vacuum advance takes care of this. Why isn't it used?

thanks

My thinking is that vacuum advance was installed to get extra advance at cruise (= gas mileage) and at idle on automobiles. Boats run with a pretty heavy load all the time, low vacuum compared to your car. All the new stuff is electronic no weights and springs to maintain. Just my 02.

Hook a vacuum gauge up and see what you are running. It will always be very low except at idle. Coming on plane likely has the same advance as 3800 with a vacuum advance. Too small of a vacuum range to adjust the timing with.

I guess that's what I was getting at. Vacuum advance would allow you to run more advance at idle (which is usually very desirable) while still keeping reasonable advance at low rpm's coming on plane. Without vacuum advance, you always end up compormising on the idle advance to avoid detonation at low rpm WOT.

Is the answer as simple as: Boaters don't care enough about idle to add another contraption?

Actually, a vacuum advance should be called a vacuum "retard". The device by not having a vacuum signal retards the timing. During starting it retards the timing, during heavy accelleration it retards the timing. They work great on cars that will cruise with minimum throttle settings but are useless on a boat because during cruising there is a very small vacuum signal. Marine distributors are designed to have less total advance range than an automobile distributor. Depending on the make, different weights and springs can be installed to customize the advance range and curve. The vacuum advance isn't needed.