1979 6hp Evinrude abruptly lost power today

Guys, I'm new to boats, but I'm trying to learn as fast as possible.

A couple weeks ago I bought a 6hp 1979 model 6904E outboard engine from a friend (200 bucks). It was supposedly overhauled recently, and was used on a sailboat (its a longshaft). Taking the cover off, the plugs and other things look very clean, there are definitely some new components in there.

I have used the engine for three 2-hour trips on the water. It has been running great. Starts on third pull, moves my 250lb body to 14 mph (by GPS). Today was the third trip, and the trouble started near the end of my trip.

The problem: After 1.5 hours of mostly full-throttle cruising, I noticed the boat seeming to go slower. I thought I might have been imagining things. Then a couple minutes later, the boat just slowed to about walking pace. Fortunately I was almost back to the dock. It eventually quit, though I got it to re-start and idle, but it wouldn't do more than that. Then I got to the dock and I let the engine sit for a few minutes. I then cranked it back up, put it in gear, and gunned the engine. Boom, full power for about 30 seconds, I made a wide circle in the harbor. Then the power went back to crap. So, whatever the problem was, it went away for like 30 seconds, then came back.

I'm running 87 octane gas with 2-stroke oil from Home Depot (the string trimmer stuff).

I got the motor home and put it in the garbage barrel with water, and cleaned off the plugs with carb spray. It would then run at full throttle in the water barrel, but still it didnt sound quite right and didn't rev up very quickly. It would die if I twisted the throttle too quickly.

What is the next thing I should check? I have a compression gauge and I'm a pretty good shade tree mechanic when it comes to cars, have swapped engines, transmissions, everything else virtually. But my knowledge on 2-strokes and boats is not much yet.

Oh yeah, I have been running the engine with the rich/lean control right in the middle.

Thanks for your help.
Adam

Re: 1979 6hp Evinrude abruptly lost power today

Sounds like you lost a cyl. Do a compression check and a spark test. Spark should jump a 7/16 " open air gap on a spark tester.

Re: 1979 6hp Evinrude abruptly lost power today

Use the proper oil rated for a marine engine.

Re: 1979 6hp Evinrude abruptly lost power today

You should be mixing the gas and oil at 50:1 and use a TC-W3 rated two stroke oil.

Re: 1979 6hp Evinrude abruptly lost power today

There is a difference between air cooled and water cooled two stroke oils, and it sounds like you are using air cooled engine oil. You should be using an oil with the TCW-3 rating on the label (the W indicating use in water cooled engines). This article is good in explaining the differences between the two oils:

http://www.ultralighthomepage.com/OIL/oil.html

Re: 1979 6hp Evinrude abruptly lost power today

If power came back up thats a good sign probably a fuel or spark issue.

Re: 1979 6hp Evinrude abruptly lost power today

Thanks for the info guys. I will get the right oil before I take the engine out again.

I just checked the compression (engine cold). 65 psi top cylinder, 60 psi bottom cylinder, throttle opened half way.

Is that normal for a 2-stroke outboard? I read another post on the internet where a guy had a cylinder in that range, and people were like "your engine is toast."

I then put the plugs back in and cranked it up. Started on two pulls, choke out on first pull. Put it in gear and twisted to to full throttle, it didn't seem to hesitate at all. I then let it run a couple minutes, brought it back down to idle. It held the idle fine. I dont know how much power its really putting out though.

Is this compression level ok?

Thanks,
Adam

Re: 1979 6hp Evinrude abruptly lost power today

pull start two strokes are difficult to get an accurate compression reading from. What you tend to do is look for less than 10% variance between the cylinders. I would say yours is a little bit low but the variance is within specs and it was taken with a cold block so it is most likely okay. You can run some Seafoam or BRP engine tuner (which is a another decarber) through it to decarb the engine and see if it loosen the rings up and increases the compression. If the fuel lines haven't been replaced you should change those out as the ethanol that is in today's fuel will break them down.

Re: 1979 6hp Evinrude abruptly lost power today

Have you checked the head temp? Was it over heating? When was the last time the water pump was changed?

Re: 1979 6hp Evinrude abruptly lost power today

etracer68 said:

Have you checked the head temp? Was it over heating? When was the last time the water pump was changed?

Click to expand...

How do I check the head temp? I don't think it was overheated. When it lost power, I put my hand on the flywheel and it wasn't really hot, but I didn't try to touch the head itself.

I have no idea when the water pump was last changed, unfortunately. I just bought it so, its possible it hasnt been changed ever.

Thanks,
Adam

Re: 1979 6hp Evinrude abruptly lost power today

hidef said:

pull start two strokes are difficult to get an accurate compression reading from. What you tend to do is look for less than 10% variance between the cylinders. I would say yours is a little bit low but the variance is within specs and it was taken with a cold block so it is most likely okay. You can run some Seafoam or BRP engine tuner (which is a another decarber) through it to decarb the engine and see if it loosen the rings up and increases the compression. If the fuel lines haven't been replaced you should change those out as the ethanol that is in today's fuel will break them down.

Click to expand...

Ok I'll look into that stuff. Thanks.

Adam

Re: 1979 6hp Evinrude abruptly lost power today

Adam10 said:

After 1.5 hours of mostly full-throttle cruising, I noticed the boat seeming to go slower. I thought I might have been imagining things. Then a couple minutes later, the boat just slowed to about walking pace. It eventually quit. I got to the dock and I let the engine sit for a few minutes. I cranked it up, put it in gear, and gunned the engine. full power for about 30 seconds, I made a wide circle in the harbor. Then the power went back to crap. So, whatever the problem was, it went away for like 30 seconds, then came back.

Click to expand...

That (edited) explanation indicates a engine that's overheating to a point whereas it starts to seize up, then after it cools slightly, regains power until it overheats again. Normally, when a engine heats up to that point, the cylinder head paint turns brownish but not always.

This could also result in a head gasket failing between the cylinders, hence the very close and low compression readings.

If it were me, I'd have a new water pump assembly installed, resurface/clean the sealing surfaces of the cylinder head and crankcase/block and install a new head gasket. Torque the head bolts 60 to 80 inch pounds in the following sequence.

9...10
5....6
1....2
4....3
8....7

Re: 1979 6hp Evinrude abruptly lost power today

Hey there fellas,
Sorry want to tag in here, I am working on the same model of outboard.
Would anyone have a PDF manual on this model?
I am replacing the impellar, how do I split the lower unit? Something (shift shaft) is hanging me up?

Again sorry to jump in here, but I ahve been following your posts the last few days. My compression reads around 80 psi & I thought that was a little low as well. But mine has been run in some time either.

Thnx Again
Hoss

Re: 1979 6hp Evinrude abruptly lost power today

Hoss... Shift that 6hp to drop the lower unit as much as possible, then remove one of the 3/8" hex head bolts you'll see in the brass shift connector near the front of the unit.

If you've already done that, rotate the driveshaft somewhat to align a top driveshaft pin with a related release slot that might be in the model.

Re: 1979 6hp Evinrude abruptly lost power today

Joe Reeves said:

Hoss... Shift that 6hp to drop the lower unit as much as possible, then remove one of the 3/8" hex head bolts you'll see in the brass shift connector near the front of the unit.

...I thought so! Thank-you Sir Joe!
I seen that nut there (it also has a slot for Screwdriver) Between the mid-section & lower unit, but wanted to make sure. There's not alot of room there to get any kind of tools in to work at it, but I will try again.
Will it be difficult to reattach?

Re: Adam10 Issue:[/B]Thanks again for letting me tag in here....
My 2 cents is start with a carb clean. Fuel does some funny & harmfull things when left sitting. I've seen some carbs all varnished up, & others crystallized, which could clog a jet in the carb.
Could also be sediment from your fuel tank being sucked up. When you shut the engine off for the 30 seconds, things are allowed to settle, then when you fire it up again it will run fine, but like you said it doesn't sound like it did when it ran fine. You can also do a plug check, if they are starting to turn white, that would indicated a "Lean" mixture (to much air) not enough fuel (due to dirty fuel system) which then you would want to get that resolved quickly, or you may end up with a trip to the scrap yard sooner than you think.

Click to expand...

Re: 1979 6hp Evinrude abruptly lost power today

Joe Reeves said:

Hoss... Shift that 6hp to drop the lower unit as much as possible, then remove one of the 3/8" hex head bolts you'll see in the brass shift connector near the front of the unit.

If you've already done that, rotate the driveshaft somewhat to align a top driveshaft pin with a related release slot that might be in the model.

Click to expand...

Hello Hoss here again,

Still having difficulty trying to separate the lower unit.
I can't seem to get enough of a gap to get any kind of tool in there to allow me to loosen the nut. Any tips & or suggestions?
I dont want to pry on the case for fear of breaking it.

Thank you in advance, any help is greatly appreciated.
Kent

Re: 1979 6hp Evinrude abruptly lost power today

You may need to slowly turn the flywheel to line up a pin in the top portion of the driveshaft with a slot that exists in the related housing. If so, that would allow the unit to drop down somewhat.

If all else fails and the driveshaft is rusted within the crankshaft splines..... that does create a problem.

Re: 1979 6hp Evinrude abruptly lost power today

Joe Reeves said:

You may need to slowly turn the flywheel to line up a pin in the top portion of the driveshaft with a slot that exists in the related housing. If so, that would allow the unit to drop down somewhat.

If all else fails and the driveshaft is rusted within the crankshaft splines..... that does create a problem.

Click to expand...

Hey Joe;

I got it figured out Now. Thanks for the help. I put a small amount of assembly grease on the splines of the shaft to help prevent the rust equation.
I had a bit of a "hickup" the shifter on the lower unit had moved upon reinstall, so that when it was shifted to reverse (it wasn't), but I got it figured out before it got too late, & I still had time for quick beer before hitting the hay.
(actually 2 hickups, but the second one was the dealer had looked up & sold me the wrong impellar) But the impellar in the lower unit wasn't in Bad shape at, looked like new, & twice the size of the one the dealer had sold me.
But it ended well & tonight it goes in the test tank.
Thanks again Joe
The-Hoss!