Acceleration problem

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  #1  
Old 06-29-10, 09:04 AM
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Acceleration problem

90 HP Force Outboard. I run this engine every weekend. Starts Just fine, runs good. When I accelerate 0-30% no problem 31-60% will stall, but if I quickly accelerate to 61% or more runs fine again. Any thoughts?

Blair
 
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  #2  
Old 06-29-10, 06:30 PM
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That's a little odd problem.

I guess I would start with the basics. Spark plugs, fresh fuel, compression test, check timing.
 
  #3  
Old 07-15-10, 12:09 PM
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I have put new plugs in it and fresh fuel. Still same issue.
 
  #4  
Old 07-15-10, 06:07 PM
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Try to get someone to pump the primer bulb while it's acting up. This will eliminate the fuel pump.

How did the spark plugs look? Where they all even colored?
 
  #5  
Old 07-18-10, 02:02 PM
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top 2 plugs were black not horrible, bottom plug was silver/brown
 
  #6  
Old 07-20-10, 07:42 PM
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I would get a compression test done just to be sure you're dealing with a mechanically sound engine.

Does the problem show up as you're getting on plane?
What happens if you're on plane, back off the throttle to the problem spot and then accelerate?

It sounds like a fuel or compression problem.
 
  #7  
Old 07-21-10, 12:53 PM
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I will try having someone pump the bulb while accelerating. I will also try backing off and accelerating again.

Let you know.

Thanks for the feed back.

BG
 
  #8  
Old 07-25-10, 06:55 AM
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Pumping the bulb while accelerating did not help.

Backing off while on plane & then accelerating again is does not act up.

Now THE ISSUE, I did a compression test:

Top 90, Middle 120, Bottom 40

I know that is not good, they should all be close.
 
  #9  
Old 07-25-10, 03:21 PM
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Your motor needs to be rebuilt, or replaced. For that low of compression there is going to be significant scoring of the cylinder walls on the low cyl.

The problem you are going to run into is parts availability. Many parts are no longer available for the force line through mercury. I personally would suggest replacing it with a newer model. I have a couple late 80's mercury motors that I run on my drag boat and I found mercury no longer sells head gaskets. I have found another source but it goes to show a very common part that they quit making.
 
  #10  
Old 07-26-10, 09:04 AM
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Thanks for all your help.

I am considering a Honda or Yamaha 4 stroke, any advice?
 
  #11  
Old 07-26-10, 08:17 PM
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You can't go wrong with ether manufacturer, if you are buying new I would chose what dealership is closer and or better service. I'm not suggesting you will have any problems but if you do you don't want to drive 2 hours for service.

Good luck.
 
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