Evinrude 35HP Outboard

[Synch]

Hello

I bought myself a boat with this motor. I think it is from 70-80s.

The problem is that when I'm on water and trying to achieve max speed then the RPMs and the speed aren't high enough. I've been able to achieve only 15 kilometers/9 miles per 100km speed but I think that this should give out more than only that.

What have I done:

Change 2 spark plugs - The correct ones per manual


What is the problem:

Outside the water, the motor on FORWARD has the top end RPMs, no hesitation. On idle it is the same.
Inside the water, the motor on FORWARD has low speed and you can hear that the RPMs are low. When I put it on idle and just put MAX choke, the RPMs sky rocket and you can hear that it should be like that on full speed ahead.

What would be the cause of this? I've been thinking about the carburator and high speed jet or maybe the full carburator is full on gunk.


Sorry if this has been answered before.

 

[CaptnKingfisher]

First I was thinking you were running on one cylinder but you gave a big clue at the end.. richening the mixture (choke) seems to solve the problem. So I would try adjusting your idle mix screw on the carburetor. You need an accurate tachometer to do this correctly. Since youre already running lean, you want to turn the screw counterclockwise and you'll see the rpms begin to rise as you get closer to the correct setting. Keep turning counterclockwise until rpms begin to drop again due to a too rich condition. Then turn clockwise (opposite direction) and rpms will climb, but continue turning until you notice rpms dropping due to a too lean condition. Now you know the upper and lower end of the spectrum. Now make your final adjustments by turning counterclockwise again until maximum rpm and smoothness is achieved. After this you probably have changed your idle speed (rpms) and you may be too fast. There is another screw to change this. Set your idle speed according to your manual, probably around 700 rpms.

Let me know if it works

 

[racerone]

Fact.-----It will rev up in neutral like all motors will.---Even in gear out of the water is really neutral as the prop does no work !!!-----Means nothing.----So what is the model # of your motor ?----I think it is running on 1 cylinder.-----Test compression , post the numbers.---Check spark.

 

[Synch]

Sorry, I have measured the compression.

One cylinder had 10 bar and the other 10.5 bar. I've thought of running the motor and then taking out the ignition coil from the spark plug to see if it works or not.

I tested once one cylinder, stoped the motor, then took out the other plug and started the other cylinder. That way everything worked.

 

[Synch]

If I'm honest

1. Idle choke is working outside and inside water the same - The RPMs are lowering and gaining the same way.

2. FORWARD gear initiated outside water with full throttle - The RPMs are identical to the Idle choke RPMs

3. FORWARD gear initiated inside water with full throttle - You can hear the RPMs aren't gaining and the speed is slow. It isn't as noisy and RPMs aren't high like outside water.

 

[F_R]

IF---if it were running normally, and you ran it at full throttle out of the water, you might be picking up the pieces. Hope you were standing out of the way. Dont do that.

 

[Synch]

This is the idle

 

[racerone]

Likely it is running on one cylinder.-----Some trouble shooting is required to find why there is no power under load.----Running it a full throttle out of the water proves nothing and may indeed damage the motor as already stated !!

 

[Synch]

I tested the motor

Took one spark plug off, started the motor. It wasn’t working and sounding as good.
Put both spark plugs on, started and it sounded better (sounded like two cylinders)
I cleaned the carburator but still the problem persists.

 

[hardwater fisherman]

I tested the motor

Took one spark plug off, started the motor. It wasn’t working and sounding as good.
Put both spark plugs on, started and it sounded better (sounded like two cylinders)
I cleaned the carburator but still the problem persists.

Did you try both cylinders? Your explanation suggests you tried just one... Check to see if both spark plug leads produce an open air spark of 7/16".

 

[Synch]

Open air, they both had the same amount of spark.

I tried running it and took one plug off, then tried the other and the sound changed, like one cylinder died

 

[oldboat1]

Seem to have water in the pan -- may need a head gasket, thermostat cover gasket, or a powerhead gasket. (Maybe another explanation?)

Get a cheap open air spark tester (adjustable) from an auto parts store -- think Lisle co. makes them. Don't get the inline closed type.

 

[Hab]

Seems to be running fairly well in the video. If your only having trouble at the top end under load, its probably worth trying to clean the high speed jets again in the carburetor. It took me at least 4 times before I really knew what I was doing.

 

[CaptnKingfisher]

Open air, they both had the same amount of spark.

I tried running it and took one plug off, then tried the other and the sound changed, like one cylinder died

The way you worded this confuses me. Youre saying the engine ran normal with one plug off, but with the other plug off you experienced a loss of rpm? This leads me to believe you have weak spark on one cylinder. Unless I misunderstand your post.

Also to my ear, watching your video sounds like your idle speed is pretty high. How about taking the plugs out and sharing a couple pics of the electrodes?

Also.. what the heck does this even mean? "15 kilometers/9 miles per 100km speed".. I'm assuming you mean 15 km/hr? Which translates to 9 miles per hour for us Yanks. How big is your boat? Is it fiberglass? Aluminum? Weight?

Tough to help from the internet, check carb linkages, make sure throttle plate opens all the way, do another cylinder drop test but note the rpms and post them here for both cylinders firing, then the rpms with cylinder 1 isolated, then rpms with cylinder 2 isolated. Need a lot more info to be able to make any progress

 

[Synch]

The boat is fiberglass, SOFA 14

Sorry, I did mean to say:

Motor working with two spark plugs, pulling one off, one cylinder dies. Putting back on, seems to start and idle better.

Would an old fuel pump be a culprit too? Seems like a original one.

 

[Synch]

This is with one plug starting

 

[Synch]

This is both plugs on

 

[oldboat1]

Run it in a deep test barrel -- plastic trash can is good, with water about half way up the leg. Sounds pretty good on 2. Let it run for five or ten minutes in gear at idle, checking temp on top of head. When warmed up, adjust the idle mix screw for best running (1/8 turn at a time). Adjust clockwise until motor pops or stalls, then back out 1/4 turn.

 

[Synch]

Hi

I put a 1000L barrel under the motor and tested it in water.
This is IDLE and CHOKE

 

[Synch]

And this is gear FORWARD and FULL THROTTLE