Evinrude 25 HP Persistent Cough . . .

[tpenfield]

The Evinrude 25 hp ( Model # E25ELCTD) that we use on the Boston Whaler has had a persistent cough for the past few years. The situation comes and goes, but never fully disappears. Warming the engine does not help much.

Here is a 30 second video of the engine running in a 100 gallon tub, coughing like no tomorrow.

It seems like the fuel mixture is igniting in the exhaust duct, which to me would indicate it is firing late when the piston is towards the bottom of the power stroke. I assume this also messes up the flow of new air/fuel from the crankcase. As you can see from the video, it takes the engine a moment to recover. If the engine is idling low, the cough will often stop the engine.

Just wondering what the typical causes are for something like this. It has been doing this for a few years.

 

[flyingscott]

That is a lean sneeze. Have you tried richening the mixture screw?

 

[lindy46]

That is a lean sneeze. Have you tried richening the mixture screw?

Agree

 

[jimmbo]

As pointed out, it sounds like a lean condition. If adjusting the low speed mixture has no effect, likely dirt/gum/varnish in the carbs low speed circuit.

 

[tpenfield]

Thanks guys . . . I'll take a screw driver to the carb and see what I can do. I am also running a heavy dose of carb/injector cleaner in the fuel mix.

 

[tpenfield]

So, would 'lean sneeze' be when the incoming fuel mixture is too lean and pre-ignites as it flows into the cylinder at the bottom of the stroke? Basically, the fuel mixture explodes in all directions, back into the crankcase and out the exhaust?

 

[racerone]

Sounds like the throttle plate might be " open too early " and that certainly makes them cough like a chain smoker.----Look into synchronizing throttle and ignition advance.

 

[oldboat1]

It's the air/fuel mix that is the issue, not the fuel ratio -- so adding a solvent to the tank won't really address the problem. (I'm not a big believer in additives anyway -- think good quality 2-cycle is sufficient at 50:1 premix.)

...air mix adjustment and link and sync as mentioned; possible carb cleaning/rebuild.

Looks like a nice Whaler ('69 - '70?)

 

[tpenfield]

1972 whaler . . . I think the engine is a bit newer.

 

[Faztbullet]

Customer s motors several years ago doing same thing (his a 35HP) and it ended up being a leaking bottom crank seal.

 

[tpenfield]

Customer s motors several years ago doing same thing (his a 35HP) and it ended up being a leaking bottom crank seal.

I thought that exhaust may have been coming out of a seal at the lower end of the power head. But it may be that is where a cowl breather is located.

I’m going to check it out tomorrow. Will try the mixture first.

 

[racerone]

If throttle plate is open too early the low speed circuit does not work properly.-----Motor will cough , cough , cough till the cows come home.

 

[tpenfield]

If throttle plate is open too early the low speed circuit does not work properly.-----Motor will cough , cough , cough till the cows come home.

Adding that to the list. When saying “throttle plate opening too early”, is that in relation to the timing advance?

Remedy would be to adjust the linkages accordingly (right?)

 

[tpenfield]

I turned the idle jet to rich 1/4 turn and the sneezing is gone. That seemed pretty easy :thumb:

 

[Willyclay]

Attaboy, it's usually the simple stuff!