Vacuum advance!

[MOP]

Has anyone ever heard of vacuum advance on a marine app?? I have not but wiling to learn.

Phil

[GeneD]

My old Pacemaker had vacuum advance, and points ignition.
These days, with electronic ignition...this is outdated and obsolete.

[Forrest]

Vacuum advance simply not needed in a marine application. All vacuum advance does in an automotive application is advance the timing when the car or truck coasts with the throttle closed (high-vacuum). Advancing the timing during high vacuum operation, keeps the engine from back-firing. Marine engines operate under very low vacuum conditions except at idle.

[BigGrizzly]

Forrest is correct to a point. Some engines actually advance to add fuel economy at a steady state cruise. Most of my stuff does this until the gas peddle id moved and back down she goes. This is why throttle rockers get such bad fuel economy. You can also depends if the vacuum hose is from ported or manifold vacuum. Unfortunately there is too much load on a boat engine to make this a good alternative as is described by Forrest. I have tried it on the Corsican and the 16, but id didn't fair too well. On the Corsican it would bridge on the point of detonation. I actually found evidence of it on the plugs and a blown head gasket. My experimentation on it is over.

[GeneD]

Crusader made their motors with vacuum advance for years. The vacuum was pulled off the carb (Roch 4bbl) from a port on the LHS of the carb.
Don't know if they still do this. But my 1974 Pacemaker had it.
It was the same set-up I had in my Corvette (1975), but without the electronic ignition.

[BigGrizzly]

Yes the early boats had it for start up and a fast idle thing. at a cruise that port had very little vacuum at a cruise. in the old boats when they failed it was almost unnoticeable.

[smbarcelow]

The V8 in my Ski Sporter uses vacuum advance.

[MOP]

The V8 in my Ski Sporter uses vacuum advance.

First excellent job of resizing your photo muchly appresiated!!!

Thinking back I have seen a very few old boats with VA, to me it makes very little sense as our engines being under constant load have very little vacuum. Thanks for the input and memories!!!!!

[GeneD]

Okay guys...here's the deal.
First off, the picture shows an automotive distributor.
Here's how it works...
Vacuum comes on at low rpm, advancing the spark.
As the rpm goes up, vacuum drops, but by this time, mechanical advance takes over. Pure and simple. But not so simple when it don't work, and you drive yourself crazy trying to locate the problem.
I blew so many pistons in my Corvette before I found broken springs in my mechanical advance unit.

[smbarcelow]

...First off, the picture shows an automotive distributor...

Correct. It's not a stock marine setup, but rather a Chevy ZZ4 crate engine.

[GeneD]

I'm wondering if the spark curve is the same as a Merc?
I'll bet it's nasty mean on the street, but...