1984 Evinrude 35 HP coughs every 3-4 secs

[stjernefodt]

Hey everyone, I'm asking this question for a friend who has a 1984 35 HP 'Rude that had worked normally until the last trip. Now when you get past 2000 or so RPMS, it starts to cough every 3 secs. To me it looks mechanical but I'm not so sure.

Spark plugs look ok, haven't done a compression check yet. I have a video of the problem to see if anyone can quickly assess the problem:

https://vimeo.com/49722273

Any info would be appreciated.

 

[Bosunsmate]

Re: 1984 Evinrude 35 HP coughs every 3-4 secs

It could be the jets in the carb, try running some seafoam or another carb cleaner through there. Also check the hoses for any air leaks right back to the fuel tank. Some of those ones that bend around the carbs crack underneath.
Most of the time in my experience with these motors its the powerpack that needs replacing if its an electrical problem but have a look for cracking on the sparkplug coils and if you have a multimeter you can check out the other parts too.
Quite a load shes moving there! so check the impellors pumping well, a too hot head can cause preignition and also coil failure. Sometimes a lot of gunk builds up behind the thermostat so the head doesnt get enough cooling or the thermostat is not opening properly. See if coughing happens when the motors cool, or try putting your motor on the head when its coughing, it shouldnt be too hot to touch
Ive watched video again on a better computer, Thats quite a loud click at 8/9secs, doesnt seem like fuel to me- seems more electrical or over heat

 

[F_R]

Re: 1984 Evinrude 35 HP coughs every 3-4 secs

Hard to tell without being there, but I think is is neither a cough, nor fuel or electrical. I think it's a worn out clutch dog and forward gear in the lower unit. If I'm right, it is coming out of gear, rotating 1/2 revolution, and slamming back into gear. You can see the motor jump when it does, as if it hit something in the water.

Put your hand on the gearshift lever when it is happening. If I'm correct, you will feel it "jump".

 

[Bosunsmate]

Re: 1984 Evinrude 35 HP coughs every 3-4 secs

Yeah im quite convinced by F_R on this one. You could drain your gearbox fluid and look for water ingress and lots of metal shavings too. Ive dropped my gearbox before and run a hose up the water intake tube to take place of the gearbox before so you can isolate the problem to motor or gearbox. The seals directly under the waterpump have failed on mine. There are two there with opposite facing lips so if you only feel one lip the other has gone.

 

[2manband]

Re: 1984 Evinrude 35 HP coughs every 3-4 secs

A dying powerpack could do what youre describing. Or a dirty high speed jet causing lean sneeze at higher rpm

 

[unleaded]

Re: 1984 Evinrude 35 HP coughs every 3-4 secs

yeah i agree with the clutch dog on this one, my 35 rude did the same thing. will only get worse