Can 2 out of 3 cylinders be dead?

[txp35]

I have a 1977 Evinrude 75 hp, and have been having trouble getting up to speed under a load. I ran the motor and disconnected the bottom 2 spark plugs (one at a time) and had no change in RPM. When I disconnected the top spark plug wire the motor died. I have good spark to all 3 plugs. I haven't checked the compression yet. Is it possible to have 2 out of 3 cylinders dead and the boat still run? Once I get going it runs good at wot.

What exactly does a "dead" cylinder mean?

Thanks for the help

 

[kenmyfam]

Re: Can 2 out of 3 cylinders be dead?

It's possible to have any combination of dead cylinders.
Do a compression check and everyone can go from there.

 

[txp35]

Re: Can 2 out of 3 cylinders be dead?

I did the compression test and I had 115, 105 and 85. I attempted the test a second time and I couldn't get the gauge above 45. The readings were 45, 45, and 35. I must be doing something wrong to get such low readings.

 

[kenmyfam]

Re: Can 2 out of 3 cylinders be dead?

What was your procedure ???
Your first set of numbers are not too good either.

 

[txp35]

Re: Can 2 out of 3 cylinders be dead?

I removed all three spark plugs and attached the compression gauge to each cylinder. I turned the motor over until the gauge quit moving (4-5 seconds)then I went to the next cylinder and repeated the process.

The second and third times I warmed the engine then followed the same procedure each time.

Would the spark plug wires arcing have any affect on these numbers?

 

["G"]

Re: Can 2 out of 3 cylinders be dead?

TXP- Sounds to me like you may have overheated or ran you engine dry of oil. Squirt some motor oil into your spark plug hole and try the compression test again. The readings should all be close (within 10% of each other). If all read under 120 you are looking at a blown head gasket or perhaps scored pistons or stuck rings. If one cylinder reads high and the next two are low it may be a head gasket. Warmth will make that worse. If the top cylinder is lowest and the readings go up from there as you go down that's not so good. BTW; Head gasket issues are easy to fix and fairly cheap. Good luck!

 

[txp35]

Re: Can 2 out of 3 cylinders be dead?

Thanks, I will give it a try in the next day or two

 

[fixmyevinrude]

Re: Can 2 out of 3 cylinders be dead?

I didn't see where you said you opened the throttle. When you check compression you should have the throttle wide open and the choke also open. You want the engine to be able to draw the air in with as little resistance as possible.

 

[txp35]

Re: Can 2 out of 3 cylinders be dead?

The first set of test I ran I didn't do that. I read the instructions then I opened it on the second set of test. The numbers in the 40's were with the throttle open.

 

[EARLS BOAT]

Re: Can 2 out of 3 cylinders be dead?

the cylinders should be with in 5 psi of each other. you may need a rebuild if the numbers are off! some people say open throttle, some say it does'nt matter. my seloc manual says to have throttle open. i would recomend you get a oem manual for your outboard if you don't have one. seloc is not that great.

 

[Sandhammaren05]

Re: Can 2 out of 3 cylinders be dead?

A weak 1970s-1980s 75 should show at least 135 psi in each cylinder, 10 psi difference indicates bad ring seal. A good 75 with good ring seat can pull 150 psi and over.

I did the compression test and I had 115, 105 and 85. I attempted the test a second time and I couldn't get the gauge above 45. The readings were 45, 45, and 35. I must be doing something wrong to get such low readings.

 

[Sandhammaren05]

Re: Can 2 out of 3 cylinders be dead?

Not necessary to open the carburetor butterflies when checking compression, but I wouldn't think of closing the choke!

I didn't see where you said you opened the throttle. When you check compression you should have the throttle wide open and the choke also open. You want the engine to be able to draw the air in with as little resistance as possible.

 

[txp35]

Re: Can 2 out of 3 cylinders be dead?

the cylinders should be with in 5 psi of each other. you may need a rebuild if the numbers are off! some people say open throttle, some say it does'nt matter. my seloc manual says to have throttle open. i would recomend you get a oem manual for your outboard if you don't have one. seloc is not that great.

Can someone send a link where I can find a oem manual. I am only finding seloc manuals

 

[Joe Reeves]

Re: Can 2 out of 3 cylinders be dead?

Spark, with the spark plugs removed, must jump a 7/16" gap with a strong blue lightning like flame.... a real SNAP! Does it?

Compression is related to the speed of which the engine cranks over. If you have a very slow cranking engine, remove, clean all related cables and retighten properly.

If compression increases, and the spark is as it should be, in all probability the carburetors need cleaning and rebuilding. Let us know what you find.

If the actual compression readings turn out to be 45 psi, you may have a failed head gasket at a minimum, OR a overhaul staring at you at a maximum.

 

[Sandhammaren05]

Re: Can 2 out of 3 cylinders be dead?

Type in Evinrude (or Johnson) Service Manual on

Ebay.com

1975-1987 are the 'same' powerhead, except that 1975 had lighter pistons and rods, a smaller skeg on gearcase (the latter also in 1976) and was faster on a V-bottom.

Can someone send a link where I can find a oem manual. I am only finding seloc manuals

 

[txp35]

Re: Can 2 out of 3 cylinders be dead?

I have good spark on all three. At least 7/16". I have cleaned all three carbs, but I haven't done a rebuild yet. I will do some testing tomorrow and post what I find.

 

[txp35]

Re: Can 2 out of 3 cylinders be dead?

I added oil to the spark plug holes and reran the compression test. I ended up from top to bottom with 120, 110, and 90. I also cleaned all the cables from the battery to the solenoid and then the starter. Compression is not as high as I had hoped.

 

["G"]

Re: Can 2 out of 3 cylinders be dead?

TXP-
The engine will run with the compression you listed but not as it should with good compression. That's a brilliant duh huh! OK, you already knew that because you stated you couldn't get power out of your motor. So now the object is to ask why is the compression low in the lower cylinders? Typically if the engine got hot, the upper cylinders would be the lower readings, not the lower ones. It is possible there is the start of a blown head gasket but it doesn't sound like it with the compression ratios you have. If two were very similar/close in readings I'd be suspicious. So next the next question is, check for varnished up rings or carboned rings. Perhaps you have some scored cylinders or pistons from lack of lubrication? Maybe the motor is just plain worn out. That engine has three exhaust ports you can take the cover off them and look inside at the cylinders, pistons and rings. Turn the flywheel until the piston is visible with the three sets of rings showing in the exhaust ports. Push on the rings with a small screwdriver. They should be flexable and move freely. If not, you are carboned up, varnished up, scored etc. You should be able to see that as you move the piston out of the port and visualize the cylinder walls.
If all that looks good you may have a broken reed or two. There is a test for that too. See what you have here first.

 

[freddyray21]

Re: Can 2 out of 3 cylinders be dead?

I didn't see where you said you opened the throttle. When you check compression you should have the throttle wide open and the choke also open. You want the engine to be able to draw the air in with as little resistance as possible.

not true. It makes no difference whether the throttle is open or not

 

[jonesg]

Re: Can 2 out of 3 cylinders be dead?

What I would try, before starting to wrench with it ..

run some seafoam to decarb the rings, they might very well just be stuck.

And rebuild the carbs with proper kits,

fresh fuel, preferably in a test can with a new fuel line and bulb.

Get the factory service manual,its simple to work on the engine with this.

www.outboardbooks.com

try ebay too.