Why don't boats have vacuume advance?? Most of my usage is wakeboarding at 2,100 rpms.On the 350 ci chevy. engine, the spark is at about 22* at that rpm. While the boat is underway, i can advance that distributor up to about 30* and the boat speeds up wonderfully. Exhaust temp comes down. (touching ex.manifold). But I don't go any faster than that so not to ping., . I undo it back to stock. So,,,, my question,,so far, no one seems to know the answers. Any one know something on this? I'm starting the proceedure to change dist. shafts with vacuume. I have found another that has done this, with great success. Thanks everyone who helps.