Vacuum secondaries are not used on boat carburetors.
JIMinFL
"Gene Kearns" wrote in message
...
On Thu, 19 Aug 2004 16:06:39 -0400, "Netsock" wrote:
"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. 
That is a somewhat untrue statement. Vacuum advance has limited
usefulness under conditions of constant speed and load applications.
Thus, at cruise, it would be of limited value. Under other
conditions, of varying speed, a vacuum advance would be useful.
--
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