1979 15 Evinrude loss of power, rough idle

[jlsjoe]

I have a 1979 15 horse Evinrude 2 cyl. Its always worked great for me including early this year. I recently took it out and it ran great for about 1/2 hour, full throttle and some trolling and then it started idling rough and killing. I headed for the dock and could only get about 4 mph out of it although at that speed it did run fine. Got to the dock ok. I realized later that I had mis mixed the fuel oil mix, had it about 16:1. (brain fart) I drained the fuel and put in fresh mix of 50:1 and replaced the plugs. Had it out yesterday and ran about 4 miles and it continues to act the same way. Rough idle, have to mess with the choke to keep it idling, and can only get about 4 mphs out of it. Usually does about 16mph with me and my two small boys and gear in it.
Any thoughts would me much appreciated.

Joe

 

[gatorhead]

Re: 1979 15 Evinrude loss of power, rough idle

I would suggest checking compression. The reason I say this is my older rude did the same thing, ran fine and then petered out. The rings let go and they did it with no warning at all. I could get it to run, but never right or full powered and then as I said it stopped altogether. Had I done a compression check I would have found it early on.

The good thing about doing the check is it is one of the least expensive things you can do, free if you have the tool It also tells you what kind of condition your motor is in before you start tossing money at parts everywhere else. Another thing I would suggest is to ohm your coils to make sure they are both good. Also look at your points. Only 3 things needed to make her run, fuel fire and compression, we went through two of 3

 

[jlsjoe]

Re: 1979 15 Evinrude loss of power, rough idle

Thanks gatorhead! You think that the fuel mistake I made may be unrelated?

 

[Rick.]

Re: 1979 15 Evinrude loss of power, rough idle

The fuel mistake was a good one. Too much oil isn't going to hurt your engine. Have you tried a new set of plugs? That much oil could have fouled them. I really think you should give a carb. kit and a very good carb. cleaning. Having to mess with the choke to keep it going is a pretty clear indication of not enough fuel on the slow speed and not getting over four MPH is an indication of a dirty high speed jet. Great motor though. I don't think it has points so you need not pull the flywheel just yet. Do the carb. and get back to us. There is a good article at the top of this forum in the Top Secret File on how to set your carb. slow speed needle after cleaning. Have you got an OMC service manual? It would be most helpful if you do. Best of luck. Rick.

 

[crxess]

Re: 1979 15 Evinrude loss of power, rough idle

Also confirm the fuel pump is not failing.

Simply take it for a run and pump the bulb when it starts to lay down. If it picks up the pump is weak/failing. If no change the pump is ok and carb needs attention.

 

[Rick.]

Re: 1979 15 Evinrude loss of power, rough idle

crxess: Good point. Never ignore the simple solutions. Rick.

 

[jlsjoe]

Re: 1979 15 Evinrude loss of power, rough idle

Thanks guys,
I have pumped the primer bulb during operation and have not gotten any change in performance, I also released the fuel tank cap in case it was not venting properly and also had no change. I did change the plugs after I changed the fuel but have not checked them since I got back from the test run to see if they are fouled. I did not get a manual with the motor but I will see if I can find one. I do not have a compression tester but I'll check on getting one. One other thing, I can achieve high rpms when in neutral but it won't crank high under load.

Joe

 

[Rick.]

Re: 1979 15 Evinrude loss of power, rough idle

Don't rev it too high in neutral it isn't good for it because there is no load. At the same time when there is no load it is much easier for it to get to higher RPM because it has no work to do. As well as the items mentioned so far, you should check the spark for both cylinders. You can but a spark checker at automotive stores and it goes inline with the plug wire and has an adjustable gap. Set the gap for a 1/2 inch and see that you have a nice strong blur/white spark getting to each plug. I get most of my manuals on ebay. Get the original OMC service manual and nothing but. Let us know what you find. Rick.

 

[jlsjoe]

Re: 1979 15 Evinrude loss of power, rough idle

Hi Guys,

I started it up in a barrel tonight and ran it about 10 minutes to get it good and warm and then pulled the plugs to do a compression test. It ran pretty well but was kind of smokey. The lower plug was very fouled and wet and the top one still looked new. This was after about 1 gallon of fuel run through it on the lake and in the barrel, mostly on the lake with new plugs. The lower cyl tested at 100 psi and the top one 105 psi. Looks like I may have a dead hole?

Joe

 

[crxess]

Re: 1979 15 Evinrude loss of power, rough idle

No, your numbers are close and should be good enough to get it running right.

Oddly, it still sounds like the fuel pump. If the diaphragm starts leaking out the back it drains into the lower cylinder. This causes over rich mix and fouls the plug.

 

[jlsjoe]

Re: 1979 15 Evinrude loss of power, rough idle

OK, by dead hole I mean't no fire. If the diaphram was leaking would it be visable? Can you tell me what the compression should be?

Joe

 

[Rick.]

Re: 1979 15 Evinrude loss of power, rough idle

No one really knows regarding compression numbers as they have never been published by OMC. Yours is very acceptable though so don't worry about it. You said the lower plug was fouled and wet. Any chance the wet was water? Did it look milky or was it just gas/oil mix? Were you able to get a spark tester? That would be my next move with what you reported about your plugs appearance. Don't worry, this motor is going to run. Rick.

 

[jlsjoe]

Re: 1979 15 Evinrude loss of power, rough idle

I don't think it was water as in was not white or milky but black and oily, stunk like gas. After I did the comp. test I cleaned the plug, reinstalled them and ran the motor for about a minute then pulled the plugs again. Top one was still good and lower one was black and wet again. Not as bad but looked pretty bad for one minute of idling.

Thanks for all the help Rick and everyone else too!!

Joe

 

[jlsjoe]

Re: 1979 15 Evinrude loss of power, rough idle

I finally got my spark tester, ordered online cause no one in town had one for sale and I think I may have not gotten what I need. It does not have an adjustable gap but rather a bulb. I could not get the bulb to flash on either hole. I think there must be current through it though as the motor did run but maybe the bulb is bad. I removed the upper plug wire, the clean plug and it started and it ran the same as before so I did the same on the lower plug, fouled one, and reattached the upper plug and could not get it to start or even fire. Looks like there may be no spark on the upper cylinder and I'm only running on the lower cylinder which is fouling really badly. Not really what I was expecting and now I'm even more confused if that is possible.

Joe

 

[jlsjoe]

Re: 1979 15 Evinrude loss of power, rough idle

I'm thinking no fuel in the top hole since the plug is always like new and dry?

 

[CatTwentyTwo]

Re: 1979 15 Evinrude loss of power, rough idle

It does sound like you got a bad spark checker, the bulb flashing can be a bit hard to see if you are in bright sunlight though. I don't know about the 79 models, but my 84 9.9 lost spark on one cylinder years ago and it turned out to be a bad coil. It would barely idle and had no power at all. Can you swap the coils on your motor to see if the problem moves with the coils?

 

[jlsjoe]

Re: 1979 15 Evinrude loss of power, rough idle

Your right ryoung. They are hard to see in the bright sunlight. I tried it tonight in the dark and the bulb glowed fairly bright orange on the lower cylinder and was very very faint orange on the top cylinder. I'm new with the spark tester but it looked like the suspect cylinder has a weak spark.

Joe

 

[jbjennings]

Re: 1979 15 Evinrude loss of power, rough idle

No doubt you're on the right track. I'd switch the coils as was advised and see if the weak spark follows the coil. If switching the coils doesn't change anything, I'd be leaning toward a bad powerpack.
BTW, as you already suspect, the reason the top plug is clean and the bottom one is oily, is because the top plug is burning off the fuel and the bottom plug is not. When the spark plug is under compression and all that fuel is in the cylinder, a weak coil won't make a spark, since the fuel is not a good conductor of electricity. No spark and the unburnt fuel causes a wet plug.
JBJ

 

[Rick.]

Re: 1979 15 Evinrude loss of power, rough idle

I would recommend you fire it up in the dark and check for spark going to ground. In the dark you can see spark so much better than in the daylight. I have to tell you I spent an exhaustive amount of time and effort on my 79 - 9.9 this spring and the problem was the bottom cylinder was too wet to fire. In the end I found a piece of plastic, broken off the slow speed adjustment knob, stuck in the reed valve. I'm not suggesting that is your problem due to the fact you appear to have weak spark and weak spark under compression could mean no spark. I have the type of spark checker you got and although useful, it will not tell you the quality of your spark. You really need to try to get the other type of spark tester if possible. Keep us informed. Rick.

 

[jlsjoe]

Re: 1979 15 Evinrude loss of power, rough idle

I hope I didn't mis speak earlier but what is confusing is that the top hole, clean and dry is the one that is not firing. The lower one, very oily and fouled looking is the one that is firing/running the moter. This is what has me confused.