"Lloyd Sumpter" wrote in message
...
On Fri, 28 May 2004 13:54:40 +0000, marbisiNsP wrote:

The secondaries really open because of THROTTLE setting, not RPM,
correct?

No they work on throttle *and* manifold vacuum.
If he goes with a steeper prop they will open sooner.

On Mon, 31 May 2004 05:38:10 +0000, Joe wrote:


"Lloyd Sumpter" wrote in message
...
On Fri, 28 May 2004 13:54:40 +0000, marbisiNsP wrote:

The secondaries really open because of THROTTLE setting, not RPM,
correct?

No they work on throttle *and* manifold vacuum. If he goes with a steeper prop
they will open sooner.

So then it's even more logical to go to less pitch: higher rpm, more power at
less throttle, AND less manifold vacuum.

Lloyd

On Sun, 30 May 2004 20:03:31 -0700, "Lloyd Sumpter"
wrote:


The secondaries really open because of THROTTLE setting, not RPM, correct? So
how about this: DECREASE your prop pitch. Then you're running at a higher rpm,
where the engine puts out more power at lower throttle setting. I suspect you'll
be able to get that few more knots to get fully on plane at a lower throttle
setting than with the "steeper" prop.

Worth a try...

I actually thought about adjusting the linkages on the secondaries so
they open at a higher throttle position; so they open, for example, at
3,400 RPM's rather than 3,200. Manifold vacuum may also be a
consideration.

I realize there's no way around inboard gas engines drinking fuel like
a teen at his/her first frat party, but there's a noticable difference
in noise and fuel comsumption when those secondaries open.

Whether going up or down in prop size, going to four blades, or
whatever other options there are, if I could get 24kts out of 3,100
RPM's with these engines, I'd be in very good shape!

On Mon, 31 May 2004 14:37:17 GMT, wrote:
I actually thought about adjusting the linkages on the secondaries so
they open at a higher throttle position; so they open, for example, at
3,400 RPM's rather than 3,200. Manifold vacuum may also be a
consideration.

=========================================

One thing you really don't want to do is lean out the engine too much.
That will cost you more in the long run than a little extra fuel. Use
the trim tabs when needed and be happy.

I definitely agree that the boat is overpropped and you could be causing
significant damage due to detonation from overloading the engine. Playing with
the secondary opening adjustment also sounds like trouble just waiting to
happen due to possibly running the motor too lean. You need to speak to an
experienced propellor shop about your options. Also, a convertion to an efi
setup although costily might help you burn less fuel at that higher RPMS that
you apparently need to achieve a desireable cruising speed. You would also
reduce engine noise from the secondaries opening with the efi setup.
Jay