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1999 Johnson 9.9 hp - Runs well except under load.

J

jmomc345

Member
Problem began occurring recently. Motor starts easily, idles and trolls well. It is on a 14" aluminum boat. With just me in the boat it takes a much longer time to get on plane but then runs at full speed like it always used to. With another person or two in the boat in goes much slower than previously.

Doesn't seem like a gas/carb issue since it runs well at slow speed and will eventually run at top speed after it planes out.

Electrical - maybe a coil breaking down when under a load?

How about the prop? I took it off but nothing looked wrong. It is possible the prop is slipping under a load? How do you test or check that?

Thanks
 
The problem you speak of (weight to hp factor) indicates that the propeller has too much pitch and the engine is struggling to obtain its proper rpm. The cure is to have a prop with a lower pitch.
 
joereeves said:
The problem you speak of (weight to hp factor) indicates that the propeller has too much pitch and the engine is struggling to obtain its proper rpm. The cure is to have a prop with a lower pitch.
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Yes, but the motor used to run fine, plane out the boat with just me and go much faster with another person than it does now. So it seems something has happened/changed recently to alter the high speed under load performance?
 
It's at a lake but the boat and motor are usually in the water only when I use it. Occasionally, it sits in the water for up to a week.
 
jmomc345 said:
Yes, but the motor used to run fine, plane out the boat with just me and go much faster with another person than it does now. So it seems something has happened/changed recently to alter the high speed under load performance?
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Okay... that wasn't mentioned prviously. If the boat has a false bottom, check it for water.

Check the compression of the engine. What are the psi readings of both cylinders?

Check the spark (with the s/plugs removed) to see if the spark will jump a 7/16" gap with a strong blue lightning like flame... a real SNAP!

If the compression and spark are as they should be, in all probability the carburetor needs cleaning, especially the brass high speed jet that is at the bottom portion of the upper housing that extends to the bottom of the float chamber.
 
If I want to check if the propeller bushing is slipping - how do I do it? I assume I should score a mark on the prop housing and the bushing and then see if it changes? Does it matter which end of the prop I use to score and check?
 
OK, I marked the prop housing and the bushing sleeve and took the boat out and then removed the prop nut and spacer. The two marks were about 1/4" apart, but I assume it has been rotating all the way around. Also, the brass end of the bushing and the spacer show wear - like they have been spinning against each other. Am I on the right track that the prop busing needs to be replaced or get a new prop? And that probably is the problem I am having with the motor?
 
If those marks were originally in line and have now moved then yes the hub is slipping and it needs to be repaired or a new prop is in order. Good luck
 
So I called the local Evinrude dealer and they said the part (386119) has been discontinued and their distributors do not have any in stock. So it looks like it will have to be a new prop.
 
jmomc345 said:
So I called the local Evinrude dealer and they said the part (386119) has been discontinued and their distributors do not have any in stock. So it looks like it will have to be a new prop.
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So check into prop rebuilders as they may have a source for the parts.
 
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