1969 Evinrude 25hp looses power at WOT

[***SAM***]

Hello,

My '69 Sporster has been running like a champ with just one or two people in my 15ft aluminum runabout. However, 4 of us went out this weekend and after 2-3 minutes at wide open we lost power. After idling/ cooling off for a while we could get back up on plane and cruise. Running wide open for prolonged periods would recreate the same situation. Could it be a heat issue?

Thanks for your insights.

Sam

 

[boobie]

Re: 1969 Evinrude 25hp looses power at WOT

Whens the last time the water pump was replaced ??

 

[***SAM***]

Re: 1969 Evinrude 25hp looses power at WOT

Less than a year ago. I had to go through the entire gear-case, so I did the pump, seals and everything at the same time. I notice when I run it on the hose, the exhaust water is hotter than I'd like. It's not very hot or would ever come close to burning your hand, but I remember it being cooler in the past, especially when I ran it in a bucket. You'd expect that though right?

 

[lindy46]

Re: 1969 Evinrude 25hp looses power at WOT

Maybe dropping a cylinder?

 

[nwcove]

Re: 1969 Evinrude 25hp looses power at WOT

you may want to check the t-stat.

 

[***SAM***]

Re: 1969 Evinrude 25hp looses power at WOT

T-stat indeed!!! Here's what I found: a tiny piece of rubber partially obscuring the bypass (looks worrying like the tip of an impeller) and a bizarre little blob of epoxy or JB weld below thermostat. I assume that's what it is, I've never used anything like that in my repairs.

Would love to know what you think.

 

[***SAM***]

Re: 1969 Evinrude 25hp looses power at WOT

I have another question regarding the thermostat. I removed the cap and cleaned it. Do I need to repaint the inside? Will zinc chromate be sufficient or does it need a heavy duty coating? I know the replacement cap is about $25 and comes pre-painted on the inside. Advice?

 

[kfa4303]

Re: 1969 Evinrude 25hp looses power at WOT

Hi SAM. No need to repaint the interior. Zinc Chromate followed by a top coat will be fine on the outside. I would figure out where the little piece of rubber from the impeller came from and to see if there may be more bits blocking the internal passages of the motor. You'll want to replace the impeller itself too, of course.

 

[tbfosback]

Re: 1969 Evinrude 25hp looses power at WOT

^^ X 2
Make sure to clean out all of the H2O tubes as well. I know it sound silly but I have seen people put them in with bits of impeller in them...

 

[***SAM***]

Re: 1969 Evinrude 25hp looses power at WOT

Thanks. Is there a standard procedure for cleaning the cooling routes? Compressed air? Vacuum? Water?

 

[kfa4303]

Re: 1969 Evinrude 25hp looses power at WOT

Compressed air and water are probably the safest and most popular methods.

 

[***SAM***]

Re: 1969 Evinrude 25hp looses power at WOT

Thanks for everyone's input! So it seems we have solved the problem. However, what exactly is happening that causes the outboard to shut down rather than just burn out when it is not being cooled sufficiently? Is there a safety feature?

 

[kfa4303]

Re: 1969 Evinrude 25hp looses power at WOT

Hello again SAM. These old motors don't have a specific fail-safe feature to shut them down when they overheat. Although, many modern motors do. As a result, it's not uncommon for these old girls to have catastrophic failures if the overheat goes unnoticed. However, it sounds like you got lucky and she died before she exploded. Perhaps the electronics got too hot and could no longer produce a proper spark. I would consider yourself lucky and simply try to avoid it in the future. Assuming the compression is still ok, everything else is pretty easy to fix.

 

[***SAM***]

Re: 1969 Evinrude 25hp looses power at WOT

I'm forever checking to see that it's pumping water and I listen to the motor constantly during a cruise. I have even shushed my passengers before so I could listen closer! I try to avoid running wide open, but this was an exception because of the extra passengers. I guess I did get lucky. Hoping it will be a quick fix. Thanks for all the advice.

 

[kfa4303]

Re: 1969 Evinrude 25hp looses power at WOT

No worries. I used to be OCD about checking the water flow too. I even retro-fitted a tell-tale onto my '66 20hp, but I think it starved the motor of too much water so I put it back to stock. Now I just listen for any changes in the motor to tell if I'm not pumping any water.

 

[***SAM***]

Re: 1969 Evinrude 25hp looses power at WOT

Good advice. I was thinking about adding a tell tale too, but maybe I won't bother now.

 

[kfa4303]

Re: 1969 Evinrude 25hp looses power at WOT

yeah, I decided to just leave well enough alone. While the tell-tale worked very well, it seemed to starve the motor of cooling water, which sort of defeated the whole point of the modification in the first place. Not to worry, in time you'll become very familiar with how your motor should sound when it's on the water.

 

[***SAM***]

Re: 1969 Evinrude 25hp looses power at WOT

The saga continues... So the impeller was fine after all. I kind of knew it should be considering I changed it less than a year ago. The debris in thermostat must have been from a previous impeller or rubber grommet. When I pulled the lower unit I noticed that the intake screen was almost completely blocked on the inside with corrosion. The outside looked clean though. This must be the root of the cooling problems.

The intake screen plug is really stuck. Is there a technique to free it? I tapped it for a slide hammer and it still didnt budge. Its currently soaking in PB Blaster.

 

[kfa4303]

Re: 1969 Evinrude 25hp looses power at WOT

Hello again SAM. Good catch on the dirty screen. That will definitely do it. I've never removed my screen, but I have had luck cleaning with PB and/or carb cleaner and a wire brush. I wouldn't bother removing the plug. The water only travels upwards from the screened entry point. Just thoroughly clean out the cavity now that you have the screen off. You should be able to inspect the water flow through the entire LU by spraying a bit of water into the cavity with a garden hose. The water should go in the screened area, up to the impeller and then ejected out of the top of the impeller housing into the copper water uptake tube and on to the motor. Here's a handy cut away.

 

[nwcove]

Re: 1969 Evinrude 25hp looses power at WOT

The saga continues... So the impeller was fine after all. I kind of knew it should be considering I changed it less than a year ago. The debris in thermostat must have been from a previous impeller or rubber grommet. When I pulled the lower unit I noticed that the intake screen was almost completely blocked on the inside with corrosion. The outside looked clean though. This must be the root of the cooling problems.

The intake screen plug is really stuck. Is there a technique to free it? I tapped it for a slide hammer and it still didnt budge. Its currently soaking in PB Blaster.

View attachment 206504View attachment 206505

i have never heard of or read about anyone getting that plug out with doing damage. jmo....but you may have been better off spending a couple of hours with a sewing needle....poking through every hole.....flushing, backflushing and repeating, until the intake and intake passage was clean and clear. you may have opened a can of worms that wont be an easy fix.