Troubleshooting poor performance - 77 Merc 200 20HP

ShastaCA

Cadet
Joined
Mar 8, 2014
Messages
7
Hello all,

Last year I replaced the prop on my 77 Mercury 200 20HP outboard after spinning the hub on the previous prop (this all happened about 1 week after I purchased the boat). The new prop is identical to the original, however, I have noticed a significant decrease in performance since about the time that this propeller was replaced. If I'm by myself in the boat, it'll get up on the plane without much issue, and top speed is about 20MPH. With another person in the boat, it struggles to get up on a plane at all... and I'm stuck at about 10MPH.

Today I started doing some troubleshooting... I checked the compression (both cylinders @ 115), and I replaced the spark plugs. I then went back to the prop thinking maybe something was wrong with its hub as well. I recalled being told that in gear it should not be able to be turned by hand in one direction. Though it takes a little force, I am actually able to turn it by hand in the direction that I thought I should not be able to turn it. I can hear the gear turning as I spin the prop, and I don't believe it's the hub is spinning. Is this normal, or should it not be possible to spin the prop when it's in gear?

Thanks for any assistance you can offer.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
39,412
In forward you might be able to turn the prop clockwise but not counterclockwise and that is normal.
 

ShastaCA

Cadet
Joined
Mar 8, 2014
Messages
7
In forward you might be able to turn the prop clockwise but not counterclockwise and that is normal.


Yes, in forward I can easily spin the prop clockwise (which I was expecting). What I wasn't expecting is that I can also spin it counterclockwise (requires some effort). I can hear the gears turning when spinning it counterclockwise. I had thought that it was impossible to turn the prop CCW when it was in forward.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
39,412
You are turning the engine over when it turns counterclockwise !!
 
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