Testing Cut-out Switch

[Buccaneer]

I was wondering at what vacuum are the OMC Cut-out switches from a 1955
RD-17 suppose to operate / ground the ignition?
I have one I’d like to test to see if it’s operational, but I don’t
find any testing data anywhere.
I don’t have a vacuum pump, but could run a hose to my Chevy carb
if the vacuum isn’t too high for the cut-out switch.
Thanks.

Prepare to be boarded!

[frankr]

Um—bear with me, I’ll have to see if I can find that spec. I know that 25-30-35-40hp motors have various specs.

EDIT: The Johnson service manual goes into great detail as to how it works, but doesn’t say at what vacuum. It only says that it should operate if running 2000 RPM in neutral and suddenly closing the throttle. Yeah, and if it doesn’t operate, you got a runaway motor on your hands. Cool.

[billy-j]

You can just put a piece of vacuum hose on it and just put the hose in your mouth and suck on it and use an ohmmeter to check from the terminal to the body to see if you have continuity when applying vacuum. The spring inside is specific to the engine year so do not use one from another year engine.

[Buccaneer]

quote FrankR:

Um—bear with me, I’ll have to see if I can find that spec. I know that 25-30-35-40hp motors have various specs.

EDIT: The Johnson service manual goes into great detail as to how it works, but doesn’t say at what vacuum. It only says that it should operate if running 2000 RPM in neutral and suddenly closing the throttle. Yeah, and if it doesn’t operate, you got a runaway motor on your hands. Cool.

Frank, I presume that if I could indeed test the vacuum switch via "mouth"
as Billy suggest, then the diaphragm most likely would be good yet,
and perhaps no further testing would be required at a specific vacuum.
It would be nice to know what the official procedure was suggest by OMC.
Last time I tried vacuum testing something via mouth I got dizzy, lol.

Prepare to be boarded!

[frankr]

I’ve tested them by mouth. Was dizzy before and still am

[nj-boatbuilder57]

but testing by mouth doesn’t confirm what spring rating you have. It only confirms that a.) the diaphragm is good, b.) the switch is good, and c.) that your mouth muscles are strong enough to overcome the spring.

Need a vac meter & the specs….

[Buccaneer]

quote NJ-boatbuilder57:

but testing by mouth doesn’t confirm what spring rating you have. It only confirms that a.) the diaphragm is good, b.) the switch is good, and c.) that your mouth muscles are strong enough to overcome the spring.

Need a vac meter & the specs….

Found this information from this old thread after searching via Google.
It’s regarding Gales outboard, but presume it’s similar to it’s cousins.
viewtopic.php?t=3415

I don’t think I can suck that hard 😮

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[Buccaneer]

Just learned that "Inches of water vacuum" and "inches of Mercury (Hg)
are two different animals.
42 to 46 inches of water equates to 3.1038 to 3.3994 inches of Mercury.

Prepare to be boarded!

[frankr]

Gale manual??!! Heck that is where I intended to go in the first place, but thought the Johnson one would be more comprehensive. Fooled again.

[Buccaneer]

Any reason why one of these budget "brake bleeder" hand
held vacuum pumps wouldn’t work for testing cut-out switches?
I’ve been wanting one for the past 30 years for bleeding brakes
anyway….. of course now, I hope my brake bleeding
experiences are about over!

https://www.ebay.com/itm/Car-Hand-Held- … SwWLFZo6z0

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[Author]

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