No power @ full throttle - Evinrude 40555 40hp

lilpig

Seaman Apprentice
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Nov 24, 2011
Messages
41
My father in law bought a used 40555. He's taken it to 2 repair shops and it still won't run right. Here's what we know they did:
1. Rewired most of it.
2. One shop said there was little to no spark in the lower cylinder. They got that working
3. One shop changed the impeller.

We took it out today and it started right up and ran fine. Ran it for about 10-15 min. I attempted to adjust what I think is the Low High knob because it was running rough at full throttle yet it did not seem to change anything.

Then we stopped for 10 min in the middle of the lake. It started fine yet we did not get any power at full throttle. I tried adjusting the Low High again and still nothing. Took it to full in and back it out 1 1/2 turns to 5 full turns. No change.

I'm thinking we either lost spark again or compression.

So I have 2 questions:
1. How many PSI should I have in each cylinder?
2. How many turns should we back out the Low High?

Here are 2 videos of the motor running when we did not have full power.
Part 1 - https://www.youtube.com/watch?v=wGnY-ADMHSE
Part 2 - https://www.youtube.com/watch?v=5MW4iHX7DiM
 

flyingscott

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the top knob is low speed only won't have much of an effect if any where you are. Sounds like its running on one cylinder check for spark and compression should be above 100 with no more than 10% difference between the 2.
 

flyingscott

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Sorry clean the carbs and when it does that pump the primer see if it changes
 

hardwater fisherman

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I have a 1976 version of that motor and more often than not with lack of power it is a spark issue. When turning the slow speed needle you need to give engine time to respond. The manual says to turn only 1/8 of a turn and wait for the engine to respond. Dont keep turning in and out so fast. And that is just for idle and slow speed ,the high speed orifice is fixed in the bottom of the carb float bowl. That needs to be very clean and free of debris. As far as compression as long as they are close to each other it depends on your gauge but somewhere at100 or above. mine has 130 on each but thats my gauge.Start the slow speed at 1 and 1/2 from gently seated.
 

lindy46

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Nov 27, 2008
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the top knob is low speed only won't have much of an effect if any where you are. Sounds like its running on one cylinder check for spark and compression should be above 100 with no more than 10% difference between the 2.

Agree - running on one cylinder.
 

flyingscott

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I think your motor also has a cutout switch that could be the problem you also have points and condensers.
 

lilpig

Seaman Apprentice
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Nov 24, 2011
Messages
41
I have a 1976 version of that motor and more often than not with lack of power it is a spark issue. When turning the slow speed needle you need to give engine time to respond. The manual says to turn only 1/8 of a turn and wait for the engine to respond. Dont keep turning in and out so fast. And that is just for idle and slow speed ,the high speed orifice is fixed in the bottom of the carb float bowl. That needs to be very clean and free of debris. As far as compression as long as they are close to each other it depends on your gauge but somewhere at100 or above. mine has 130 on each but thats my gauge.Start the slow speed at 1 and 1/2 from gently seated.

Ok. When I turn it in to closed, do I back it out only 1/8 and wait? Or do I back it more and only turn it 1/8 turns?
 

racerone

Supreme Mariner
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Dec 28, 2013
Messages
36,047
You back it out 1-1/2 turns.--Then adjust from there.----Most carburetor " trouble " turns out to be something else.---So test for good spark and test compression.
 

F_R

Supreme Mariner
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Jul 7, 2006
Messages
28,195
Cut-out switch cannot do anything unless motor is in run-away condition. Unless the spring in it is busted, which is extremely unlikely. What is highly likely is that it is running on one cylinder. And not because of the cut-out switch. Check spark and when you find you don't have any on one wire, check breaker points. Oh, and on the "duh" side, check spark plugs!!
 

Sunken Ship

Petty Officer 1st Class
Joined
Jun 19, 2014
Messages
252
I have 40554. This is what I did to diagnose and determine a no-fire issue:

Let it idle (maybe a little higher) then use a hammer with a wooden handle to pop one plug wire off to check for spark. If it dies then that cylinder is not firing. You will need to shut the engine off to put that wire back on then restart and repeat the same test on the other cylinder. The carb seems to be doing a good job delivering fuel from the videos to me.
 

flyingscott

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If you look at what he said they rewired it and fixed a no fire in the bottom cyl check the cutout see if they bypassed or did something there.
 

racerone

Supreme Mariner
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Dec 28, 2013
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Post # 11-------If you pull a plug wire off and the motor dies then that cylinder is firing.---It is the other cylinder that has a problem !!!!
 

David Young

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Jul 12, 2015
Messages
485
Just letting you know, you can rent a compression gauge from most auto parts store for 'Free'. Pay a deposit and you get it back when the gauge is returned.
 
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