Engine Acceleration Problems

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Mar 14, 2006
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Wilmington, NC
I have a 115 HP Yahama 2 stroke on the back of my 18' Parker. Every now and then when I accelerate all the way, the engine sounds like it is bogging down and not running at full speed to the point where the boat will not come up on plane.

I just remembered that the day this started happening I bumped a sand bar pretty hard while the engine was running as I was pulling out of a creek.

A friend has told me I may have stripped something in the lower unit so that when I accelerate, the propeller cannot catch up with the speed of the lower unit as it is stripped.

Has anyone else experienced this or heard of this??
I think your friend is confusing a spun prop hub with your engine bogging down. A spun propeller hub will do what he says, it will slip when under hard/fast acceleration. But usually, in my experience, once they start to go - they go. You should note an increase on the tach as the RPMs should be increasing as you pour on the throttle.

If your OB is stumbling and the tach doesn't go higher or is bouncing (if not going lower) than it's one of the big 3, e.g., fuel, air, or ignition. To me it sounds like a coincidence that it started appearing after the sandbar hit, but who knows. It could be water in the fuel or a coil or powerpack breaking down, but it could be in the carbs. I'd need more info to diagnose via cyber-space.

Let me ask, have you ever decarboned that OB or cleaned the carbs? If not, read through this "How to Decarbon that Outboard" by Dunk, a note marine surveyor and OB guru, click here.

Since that motor has carbs, I'd use Seafoam's "Deep Creep" aerosol spray ($6 @ NAPA auto parts) and spray into the carbs. Make sure to use the "rest" period as Dunk mentions - as that's when the solvent works and does its magic.
I appreciate your help greatly. I think you are right about it not being the spun prop. The engine has the acceleration problem every so often, not every time I accelerate.

I have never cleaned the carbs and just bought the boat used. It may have sat around for a while without being run. The gas that was in the gas tank when I bought it is also probably old.

Isn't there also some kind of additive I can pour in the gas tank that will also clean the carbs as the fuel is burned??

Thanks for all your help.
Can anyone give me a little guidance on how to spray the sea foam in my carbs?

I've located the carbs in the engine but not exactly sure how/where to spray the sea foam in the carb. I'm by no means a mechanic and I don't want to just start taking apart the carb seeing how I don't know what I'm doing. (I don't have an owners manual either as I bought the boat used).

Any advice would be great!!!