Unless you are watching them you really don't know when 4 barrel secondaries
are open or how much. Quadrajets make a noise when you open the throttle
wide at lower rpm's and you hear the extra air flow on the secondaries. But
gently opening the throttle to increase speed can result in the secondaries
opening some and not making any noticable difference in sound.


"Bowgus" wrote in message
news
I dunno but here's about how mine (Rochester Q-jet) works which seems ok
to
me. From a stop (alpha outdrive) with trim all the way down, I open the
throttle at say a count of 1000, 2000, 3000. With the trim down, the boat
comes up onto plane flat ... the bow does not point up. At about 2300 rpm
I
am on plane and around about 2400 rpm (since the engine's under load) I
hear
the secondaries opening (and if I go out tomorrow I'll check that) . If
I'm
just going to cruise, I throttle back to about 2300 rpm while
simultaneously
setting the trim for best speed/rpm which works out to engaging the trim
(up) button for about a second (count of say 1000). And from that point
on,
I won't hear the secondaries open unless operating close to WOT which is
about 4000 rpm with the 23" prop and about 4300 rpm with the 21"prop. So,
for me I'd say it's about 2400 rpm coming onto plane but I'll check that
next time out.

"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.

"Mike Harrison" wrote in message
om...
Hello group, hopefully a simple question:
For a four-barrel carb, at what RPM setting should the 3&4 barrels be
set to open at? For example should they open when attempting to climb
onto plane, and then once on plane, throttle back and plane with only
1&2 open?