"JamesgangNC" wrote in message
hlink.net...
Vacuum secondaries will come on when you demand enough to cause them
to.
Mechanical secondaries will come on based on the the throttle
position.
RPM
has nothing to do with either.

Not entirely correct...only if the weight, or drag changes on the boat.

Because water is the same thickness, and always flat, there is no load
change to effect vacuum secondaries...unless one of the previous mentioned
situations are present.

Vacuum secondaries (on a boat motor) will always open at the same RPM every
day, in relation to throttle position, unless there is more...or less
resistance.

This is also why boat engines don't need vacuum advances...the never go
"uphill", or operate in pea soup.


--
-Netsock

"It's just about going fast...that's all..."
http://home.insight.rr.com/cgreen/