Engine idle setting

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sti1471

Petty Officer 1st Class
Joined
Aug 2, 2011
Messages
312
When I hook my 80 HP outbord motor up to the flush muffs and start the engine, it idles around 1000 - 1200 RPM. As I adjust the RPMs it will get to about 900, but any lower and the engine dies.

My question: If the engine idles at 900 RPM out of the water, will it idle at 900 RPM in the water, or does it drop a certain amount when in the water? What usually is the drop amount of RPM out of the water V.S. in the water?

Thanks.
 
G

gwukena

Petty Officer 2nd Class
Joined
Apr 8, 2010
Messages
167
Re: Engine idle setting

Going to be lower once in the water due to backpressure from water at prop exhaust.
On my 83 115 drops approx 200 to 300 rpm once in water.
 
79Merc80

79Merc80

Senior Chief Petty Officer
Joined
Nov 22, 2007
Messages
673
Re: Engine idle setting

I made a "Muffler" for outboards that simulates in the water back pressure as well as the sound of the engine running in the water (Which your neibors will appreciate). Pictured below. It's easy, just 3 peices from the local hardware store.
 

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sti1471

Petty Officer 1st Class
Joined
Aug 2, 2011
Messages
312
Re: Engine idle setting

And this allows the exhaust to escape the engine still with it being a tight seal?
 
79Merc80

79Merc80

Senior Chief Petty Officer
Joined
Nov 22, 2007
Messages
673
Re: Engine idle setting

The exhaust escapes just as it would if it were in the water. The relief ports at the top of the mid tower are designed for just that purpose. Water also does drain around the prop.
 
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