Mercruiser surges when hot

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  #1  
Old 07-17-06, 01:12 PM
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Mercruiser surges when hot

I have an '85 Mark Twain 210SF with a 4.3L V6. After I run at cruising speed for 30-40 minutes, the engine loses power. When you slow down, it surges very bad.
I have a clear fuel filter at the carb and it is still full of fuel.
Any suggestions?
 
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  #2  
Old 07-17-06, 09:40 PM
Pwrbait
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What is the temp when this starts, are you overheating at all? When it surges, does it go from high rpm to nothing, then back to high, or does it act like it's just about to run out of gas? Does it do it no matter how much fuel is in the tank, or just when it reaches half a tank? Does it die, or will it keep running like that? Give us everything you can.
-Chris
 
  #3  
Old 07-18-06, 05:02 AM
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What is the temp when this starts, are you overheating at all?

It is not overheated. It usually runs about 120

When it surges, does it go from high rpm to nothing, then back to high,

Yes

Does it do it no matter how much fuel is in the tank, or just when it reaches half a tank?

I don't think it makes a difference...it's been doing it all year..I haven't had it out much but it did it at full tank and now it is down to 3/4 (holds 52 gal) and does it.

Does it die, or will it keep running like that?

It does die...especially when trying to idle or dock....needs about 1/2 throttle to keep going.

Thanks,
 
  #4  
Old 07-19-06, 02:32 AM
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Sounds like your timing chain is jumping. I had a very similar experience with a 351 Cleveland. It would maintain at half throttle or lower, but when I went to higher RPMs, it would do just what you are describing. If you don't have a chain, your belt is stretched and it's jumping. I could be wrong here, but that's what it was in my case.
Chris
 
  #5  
Old 08-08-06, 10:10 AM
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Problem solved

Well, I replaced the dist cap, rotor, plug wires and coil and it still surged after I ran 3000 RPM for awile so I cleaned the antisiphon valve and blew out the gas tank vent. Still surged. Finally found the problem.....I had replaced the inline gas filter and had tightened the hose clamp too tight and crimped the fuel line.

Oh well, I guess a 20 year old boat needed the maintenance anyway.
 
  #6  
Old 08-09-06, 06:56 AM
Pwrbait
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lol. I know it's a relief to get it fixed, but doesn't the simple things you miss just irk the $%#* outta you. Glad you got her going.
-Chris
 
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