1979 evinrude 70 sluggish after 10 minutes

Mudflap33

Recruit
Joined
Sep 5, 2016
Messages
5
Already ruled out fuel and electronics, 10 minutes in drops to half power, stop put it in reverse , full throttle for 1 second, then runs fine again whats wrong also on muffs exhaust is through foot no exhaust through mid section, when hot no exhaust through foot, what gives or is this normal
 

StarTed

Senior Chief Petty Officer
Joined
Jul 14, 2015
Messages
694
Could you be getting water in from your exhaust manifold? Check your spark plugs for water.

Really I have no idea but just a thought.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Any chance you are getting surface weeds wrapped around the prop? Reversing prop thrust certainly cleans them off.
 

Mudflap33

Recruit
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Sep 5, 2016
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5
Ok a friend just told me the throttle cable also controls the advance on the engine. .meaning as you give more throttle the engine otor advances more is this correct
 

Mudflap33

Recruit
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Sep 5, 2016
Messages
5
Good thoughts on prop but 40 ft of water..also is there some water diversion flaps in the mid section or lower unit
 

interalian

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Joined
Jul 23, 2009
Messages
2,105
Ok a friend just told me the throttle cable also controls the advance on the engine. .meaning as you give more throttle the engine otor advances more is this correct

Yes, moving throttle forward increases timing advance as it opens the carb butterflies. Direct mechanical timing advance only on these.
 

interalian

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Jul 23, 2009
Messages
2,105
Good thoughts on prop but 40 ft of water..also is there some water diversion flaps in the mid section or lower unit

There are small baffles near the exhaust relief ports high on the leg. At idle in the lake, most exhaust will go through these along with a mist of water. At higher running speeds the majority of the exhaust will exit underwater through the prop hub. When idling on muffs, the exhaust will come through the prop hub as there is no backpressure.
 

interalian

Commander
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Jul 23, 2009
Messages
2,105
Next time you lose power, try pumping the primer ball. You might have a weak fuel pump.
 

interalian

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Jul 23, 2009
Messages
2,105
Ok iterilian what would be the most common failure..cable? Sensor?

Not sure what your question is. I'm suggesting the pulse fuel pump is a bit weak and after running for a while can't keep up with demand. Pumping the primer ball will refill the carb bowls if you're running short on fuel and prove weakness in the fuel pump, or perhaps a leak somewhere in the lines.
 
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