1990 70 HP Evinrude

T

tgluvna

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Jul 4, 2007
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My motor has a power loss at high rpm. It starts fine, idles fine, accelerates good. As full throttle it sputters a little, at 75% and under it runs fine. At full throttle, when I push the choke, the sputter disappears and it gets full power for a few seconds. Gas is fresh, carbs rebuilt, plugs new, lower end oil ok too. I did take a compression reading today, 100, 100, 115. Any ideas?
 
tashasdaddy

tashasdaddy

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51,019
Re: 1990 70 HP Evinrude

when the carb were rebuilt, were the high speed jets removed with the special tool? suggest doing a decarb with seafoam, to try to get compression up a little.. it's ok but a little getting on the low side.
 
hoeser

hoeser

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Jun 18, 2006
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Re: 1990 70 HP Evinrude

Try priming your fuel bulb by hand and see if it reacts the same way as when you push the primer when you are losing power. Could be weak fuel pump. Also agree with Tashasdaddy, your compression numbers aren't great and the 15psi variance can cause issues. Decarb time, maybe replace the head gasket if that doesn't help.
 
T

tgluvna

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Re: 1990 70 HP Evinrude

I did the decarb with seafoam and wow!! The motor runs clean and much stronger all the way up and down. Thanks for the advice. I did a compression check and compression did come up a little, 105, 105, 120. I did 3- 15 minute run, 15 minute rest with 3/4 gallon gas- 1 can of seafoam. Is the compression difference something to get concerned over. Is there any easy repair?
 
T

tgluvna

Recruit
Joined
Jul 4, 2007
Messages
3
Re: 1990 70 HP Evinrude

I did the decarb with seafoam and wow!! The motor runs clean and much stronger all the way up and down. Thanks for the advice. I did a compression check and compression did come up a little, 105, 105, 120. I did 3- 15 minute run, 15 minute rest with 3/4 gallon gas- 1 can of seafoam. Is the compression difference something to get concerned over. Is there any easy repair?
 
iwombat

iwombat

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Jul 12, 2006
Messages
3,767
Re: 1990 70 HP Evinrude

If the seafoam decarb made that much difference it might be time for a seafoam/deep creep/OMC power tune soak through the spark plug holes.

Tilt motor up. Get a cylinder to TDC and squirt a bunch of <whatever> into the cylinder. Let it soak overnight at least. Repeat with all cylinders.

My guess is those two low cylinders will get closer to the high one.
 
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