How does the boat know - Lake Water or Muffs?

[samm835]

I have a 94 3.0 OMC/Cobra, yes I know there are plenty here who hate them......but to my question. Took it out last weekend for the first ride of the year. In my driveway on the muffs the motor idles perfectly, Sunday on the lake it idle'd fast. I know how to fix, but I am curious on why its different. It really shouldn't be different should it? I know this isn't an OMC thing cause my other boat which had a 3.7merc/alpha one did it when I first bought the boat. Thanks

 

[Randy169]

Re: How does the boat know - Lake Water or Muffs?

The engine won't know the difference between Lake Water or Muffs. The only difference would the pressure of the water coming in through the muffs - being that is city water.

I know when I am hooked up to city water through my fake a lake, it takes forever to warm up and my heater doesn't really work. But out in the water, no problems.

If it were simple, anyone could do it!

 

[captk]

Re: How does the boat know - Lake Water or Muffs?

first guess is no back pressure on the exhaust. second no load on the engine in the drive way. That is why boats must be tested underway.

 

[Don S]

Re: How does the boat know - Lake Water or Muffs?

The engine won't know the difference between Lake Water or Muffs.

Oh yes it will. When in the water, there is a lot more exhaust back pressure.
Load is everything above idle rpm.


Oops, failed to read Captk's replies before I replied.