Hello I am a new member to Endless Boating. Here is my problem, I own a 1977 4winns 16 foot I/O 140HP. Nice little boat. I did not run it last year. This year (last 2 weeks) I replaced the starter, points, cap, condenser and coil. Runs good so I took it out on the lake. At 4000 to 4500 RPM after it was warm the engine would rev up and we would start to lose power at the propeller. I have a Clymer Manual and can't find anythinng in there. I am thinking the shift cable is out of adjustment. Anyone hear of this before? Thanks for any feed back. Phil
Eng revs but loses power
- Thread starter 86wing
- Start date
Fun Times
Active Member
One of a few things may be going wrong with it, Either the hub inside the prop is giving out or the engine coupler is giving out.
If it's not the drive it would be the engine coupler or the prop hub. If it has a rubber bushing style prop hub you might be able to check it for any signs of mislignment by pulling the prop off the drive, Or some times by looking at the front of the prop, (spline area vs. aluminum center of prop (hub). You could test it by putting some paint marks on both the prop shaft or nut and then on the prop itself inline and go run the boat again, And see If the marks stay aligned... If Prop paint lines stays the same then it should be OK, Then another thing you could try is, See If you can, reach to the back side of the engine (not running) and see if you can feel the back of the bellhousing it will have an opening about 3 or 4 inches across. stick your fingers in there. If they come out with the stickiest, nastiest, black stuff on them like burned rubber you may need a engine coupler and the engine will need to come out to install a new coupler. One other thing you could try but it may not tell you much because it is happening at 4000 rpms and that is a lot of pressure, But some times while on the trailer you could with engine off put the drive in gear and spin the prop by hand it should lock up one way and spin ok the other way then put it in a different gear and it sould lock up the other way the prop was spining. If you can get it to spin by hand in gear with pressure then you might be able to see if it is the prop hub or the engine coupler Or maybe even the drive itself.
Other possibilities are something in the lower unit shift parts.
I believe the Prop should ratchet CCW and lock CW in reverse.
And if the upper gears in the drive are trashed the prop will work (ratchet) as it should some times or it could just lock up.
Fun Times
Active Member
Also I for got to say you could be getting some prop Blowout, It occurs when the ratio of air to water around the propeller gets so high that the propeller is no longer grabbing water, but it is trying to propel itself through air (or a relative vacuum). This causes the propeller to lose "bite", and then a chain of events occurs that can range from merely a "loose" steering feeling, to a vicious turn to the right (typically) Or lose speed and just rev's the engine could happen. The speed at which this occurs varies with boat design, gear case design, and propeller design.
Cavitation: The formation of voids or air inside the water stream, caused by low pressure near a surface. Encountered when the water separates from the propeller. Also called ventilation; causes propeller burn, and can lead to blow-out.
- A few Questions for you.
- 1 Is your prop in good shape?
- 2 Is the Anti-Cavitation Plate in good shape?: See Anti-Ventilation plate: Anti-Ventilation plate: The horizontal web or plate above the Lower Unit. It is intended to prevent the Prop from sucking surface air, Ventilating, into it and causing a Cavitation like effect. Useful on a deeply mounted outboard or drive unit.
- 3 Do you have the drive all the way down?
- 4 When dose it do it, While turning, Going straight, While triming the drive up, Ect,
Cavitation: The formation of voids or air inside the water stream, caused by low pressure near a surface. Encountered when the water separates from the propeller. Also called ventilation; causes propeller burn, and can lead to blow-out.
- A few Questions for you.
- 1 Is your prop in good shape?
- 2 Is the Anti-Cavitation Plate in good shape?: See Anti-Ventilation plate: Anti-Ventilation plate: The horizontal web or plate above the Lower Unit. It is intended to prevent the Prop from sucking surface air, Ventilating, into it and causing a Cavitation like effect. Useful on a deeply mounted outboard or drive unit.
- 3 Do you have the drive all the way down?
- 4 When dose it do it, While turning, Going straight, While triming the drive up, Ect,
Happens when going straight. I prop is a little banged up. I am putting on my other one, in good shape and taking back out. It didn't happen until after we had been out for a while. I have a larger aftermarket cavitation plate on it and it is secure. Drive was all the way down while it happened I raised and lowered the drive to see if it made a difference but it didn't.
If the engine is running fine and then you start to lose power and the engine revs increase, perhaps the hub in the prop is starting to slip. IF that's the case, I would try changing the prop to see if that cures the problem.
Hopefully you have a spare prop you can try.
-Chris
I'm not sure what prop you have but...
On many there is a hub that is pressed into the center of the prop. What can happen, is that the hub can sometimes start to break loose and then slip under load.
So that's why I was suggesting you try another prop, to see if that clears up the problem. If it does great, if it doesn't then you most likely have to look to the problem being related to something else.
Let us know how you ultimately make out.
-Chris
On many there is a hub that is pressed into the center of the prop. What can happen, is that the hub can sometimes start to break loose and then slip under load.
So that's why I was suggesting you try another prop, to see if that clears up the problem. If it does great, if it doesn't then you most likely have to look to the problem being related to something else.
Let us know how you ultimately make out.
-Chris
