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Author Topic:   Muffler for flushing
Robob2003 posted 02-01-2004 04:00 PM ET (US)   Profile for Robob2003   Send Email to Robob2003  
My brother who is an engineer made me a muffler for use when flushing my old Johnson 100 HP while using earmuffs.

It's made out of PVC pipe with an end cap drilled with numerous holes to allow the exhaust to escape. It has a tapered collar and fits into the exhaust cone in the prop. It does a good job of silencing the outboard racket out of water.

My question is whether there is more back pressure created than when the engine is in the water and if so, will using it harm the engine? I can see exhaust coming out of the small side ports in the gearcase ahead of the prop which I think are for water passage and exhaust scavenging when running at speed.

Thank you in advance,

Bob on Tampa Bay

Robob2003 posted 02-04-2004 09:46 AM ET (US)     Profile for Robob2003  Send Email to Robob2003     

Any ideas out there???

Tom W Clark posted 02-04-2004 10:54 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
I doubt there would be a problem. I suspect the back pressure created by an outboard being in the water is far greater than the pressure created by this muffler.
Salmon Tub posted 02-04-2004 12:48 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
I have always used a washtowel. Just place it over the hub and put a bungy around to keep in place. The towel gets wet from the water coming out of the exhaust, silences the sound, does not create excess back-pressure, and catches all the oil, smoke and crud from the exhaust. If your worried about pressure, just keep an eye on the RPM's, should only drop about 200 rpm with muffler on.
Bigshot posted 02-04-2004 03:03 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Bob can you send me a pic....I need to make one.
Robob2003 posted 02-04-2004 04:01 PM ET (US)     Profile for Robob2003  Send Email to Robob2003     
Thank you for the help.

Salmon Tub, the wash cloth sounds like just the ticket for my neighbor, who likes the muffler but his prop hub is too big for a good fit.

Bigshot, you've got mail:-)

keltonkrew posted 02-04-2004 04:39 PM ET (US)     Profile for keltonkrew  Send Email to keltonkrew     

Can you send me a pic as well.


5 mi E of Milwaukee posted 02-04-2004 06:57 PM ET (US)     Profile for 5 mi E of Milwaukee  Send Email to 5 mi E of Milwaukee     

There is a gadget called the “Flush Muffler” sold (among other places as well, I assume) at Overton’s. See their website for a picture.

Essentially it is a collar made of what looks like a rubber pluming adaptor for going between two sizes of pipe. It muffles by having a plate held across the end by springs. The directions tell you NOT to adjust the spring pressure, which leads me to guess they’ve figured the pressure needed to simulate water pressure at normal in-water operating conditions.

I have one and I, as well as my neighbors, love it. My 90 HP “classic” carb’d 2 stroke Merc is quiet enough to talk over while standing by the stern, quieter than most lawn mowers.


Robob2003 posted 02-05-2004 09:41 AM ET (US)     Profile for Robob2003  Send Email to Robob2003     
I've been 5 miles east of Milwaukee many times but only sailing or fishing:-)

Overton's looks interesting but the ad appears to say the spring pressure is to _assure_ back pressure to flush the system thoroughly.

If I just use the earmuffs there is no back pressure. I guess it's not a problem as I get good flow through the thermostat discharging warm water.

I will send pics to those who have asked for them. I hope you have DSL or some other high speed connection because it will take a dial up a looooong time to download.

Bob on Tampa Bay

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