[maxinedougherty]

A friend of mine just bought a older bayliner this past summer without saying anything to anyone. He thought it was a good deal! The person that sold him the boat started it up on muffs and my buddy thought it ran well, He called me when he got home and I asked if he did a compression test or anything and he said NO. He took it over to pike lake and and could not get the thing to go over 10 mph. Then he had to oar it back in because it ran so crappy. I went and looked at it and the bottom cylinder had 35psi compression and the the other two were 90psi. The carbs looked like crap. He thought just because it idled okay on the muffs it was a good buy.. He regrets his purchase now I tell you!

[lobo235]

It’s not a lot but it made a world of dfference when I test ran a new Honda 9.9 at the Dealer in 2007. The motor ran great on the muffs but when I took and tried the motor on the boat it would not idle and wouldn’t take throttling up no matter what I tried. Long story short test your motor on the boat under normal conditions ex. depth and load. [links]

[oUmber]

Conversion of inches of water column to pounds per square inch is 1” of water column is equal to 0.0361272918274 PSIG. So the PSIG (pounds per square inch gauge) at a prop 15” below water is 0.5419093774111843 and 20” below water is 0.7225458365482457. [links]

[translator]

Think of it this way. Under normal use the exhaust through the prop is anywhere from 15” to 20” below water on boats with 20” and 25” transoms.

[geebus]

That is why you see "Most" marine shops will have a tank or a pond on the property to run the motor.

[Gatsu]

more

[Andreas Schildbach]

I’ve been told anything much above idle is too much, may up to 800-1000 rpm safely?

[hamiltontak]

The SELOC manual recommended instead using a barrel or trough full of water (like people mentioned above) to run the motor above idle speeds instead of on the hose with flushing muffs.

[GhoulBalliz3x]

That's why I'm interested in higher RPMs in the backyard. Not to flush. But to troubleshoot/verify repair attempts. more

[jwalck]

Even though the water pump does circulate water throughout the engine, outboards also rely heavily upon forward movement to help force water throughout the cooling system. Being on the muffs with just household water pressure is not enough to circulate fresh water throughout the motor at higher RPMs.

[hauns]

So it sounds like if I want to run hard and long I need a load, not muffs?

[Davex]

Idle only and run it long enough to were the Tstat opens. You can tell by feeling the discharge water temp. more

[TopSoil]

Why you think you need to run it at high RPM is another issue. more

[PureIt]

For every "old wive's tale" there's an old wife. here

[dishwara]

Interested in actual experiences/reasons myself due to the number of times this has been repeated. [links]

[freetx]

You can run it at any RPMs without the prop as long as you don't exceed max RPM of the engine. Would love to hear people's theory that you HAVE to have a load!