'76-40HP Evinrude: No Fire on Top Cylinder

[Sunken Ship]

I have been having some sporadic trouble from this OB (40HP Evinrude) for some time now. The motor just wouldn't take off. At WOT it would wind up to about 20-30%power.

I wanted to confirm fire on both cylinders, so I started looking around. With the engine at idle, I pulled the top plug wire from the coil and there was no change in how the motor was running-badly. I put that plug wire back on and then pulled the bottom plug wire and the motor died instantly. Did the same thing again with the same results.

Next, I disconnected the connector (green wire) to the top coil and I could feel an electrical pulse in my hand (rapid) from the wire with no change to how the engine was running. I had the same results (rapid pulse) from the green wire to the bottom coil, but the engine would die when this wire was disconnected. With this, I diagnosed a bad coil and put one on order.

Brought the boat home and pulled both coils performing resistance and continuity on the primary and secondary windings with the exact same results on both coils. Now I am wondering if the coil is really bad or not...?

Since the motor is so old I ordered an ignition tune-up kit. Sure it won't hurt.

I checked the service manual to see if the cut-out switch might be shutting the cylinder down, but that controls the bottom cylinder, so I am determining that is unrelated in this case.

Appreciate any educated opinions on this. Painfully waiting on coil to arrive.

Thanks.

 

[gm280]

This is odd. I responded to another '76 40HP Evinrude thread yesterday... Usually before you order parts, you swap out the coils and see if the problem follows the supposedly bad cols. If so, then the coils is bad, if not, then there is something else at fault... That way you've verified a bad part and don't waste money for no reason... I have the '76 40HP Johnson version of that engine that I totally rebuilt. You can see that if you like by clicking on the link below. JMHO!!

 

[Sunken Ship]

Thanks for the response. That was me in the other thread.

I posted pictures for you of my motor in my other thread about a fishing reel.

Thought about swapping the coil on the water, but kind of a pain to get to while on the water.

I have certainly checked out your motor and love it! Looks absolutely great!

I also checked-after driving around for a few minutes at low speed-how warm the spark plugs were. The top cylinder was cool whereas the bottom plug was warm. There was notable a difference in temp.

 

[hardwater fisherman]

I have had the same motor now for 8 years and have lost spark once on top and twice on the bottom. The motor has 2 original coils with cracks ,and every time it was because of dirty points. Also I have had better luck with NGK plugs.

 

[Sunken Ship]

I have had the same motor now for 8 years and have lost spark once on top and twice on the bottom. The motor has 2 original coils with cracks ,and every time it was because of dirty points. Also I have had better luck with NGK plugs.

Thanks for posting your experiences. Mine have cracks too and I think they are the original coils as well. I cleaned the points a couple of weeks ago, but ordered an ignition tune-up kit just to put fresh points on this thing. I am told people used to keep an extra pair in their cars back in the day because they were so troublesome. All the time, I am told, people were on the side of the road changing these things out. Either way, I am going to get to the bottom of this! lol

Do you mean to say you have a '76 40hp evinrude/johnson like GM280 and I? How did yours run when it stopped firing?

 

[hardwater fisherman]

Yes it is a 76 evinrude 40hp.When firing only on one mine will start and idle but no power. I use champion plugs in other omc outboards I have, but for this one they would foul very quickly.

 

[Sunken Ship]

Yes it is a 76 evinrude 40hp.When firing only on one mine will start and idle but no power. I use champion plugs in other omc outboards I have, but for this one they would foul very quickly.

Mine is idling OK too. My motor runs up to about 20-30% power and then acts like it is starving for fuel, at which point it will fall back to near idle and struggles to stay running.

I guess I will hurry up and wait on the mail truck.

 

[gm280]

Mine is idling OK too. My motor runs up to about 20-30% power and then acts like it is starving for fuel, at which point it will fall back to near idle and struggles to stay running.

I guess I will hurry up and wait on the mail truck.

Sunken, I did change out everything under the flywheel AND two new spark coils as well. One of mine was absolutely blown out, as you probably already seen, and the other one looked newer. But rebuilding this engine I decided to just replace all the ignition components so I wouldn't have any issues to need to remove the flywheel again. Don't know if you have removed your flywheel, but it doesn't just fall off there. Post back here after you replace those parts so we can see how well it works now... :thumb:

 

[Sunken Ship]

I took it out today and had the same problem, so I changed the coil on the water...no luck it ran the same.

Might clean the points and try it out to see if that solves the problem. If it does then I will put the ignition tune-up kit on.

Hopefully the ignition tune-up kit will come soon.

 

[gm280]

I took it out today and had the same problem, so I changed the coil on the water...no luck it ran the same.

Might clean the points and try it out to see if that solves the problem. If it does then I will put the ignition tune-up kit on.

Hopefully the ignition tune-up kit will come soon.

Luckily with the type ignition system if you have fire on one coil and not the other, you know the exciter coil is working properly because it feeds both cylinders. So either the points or condenser is not doing its job correctly, because you already swapped coils and still no spark.

 

[Sunken Ship]

Thanks for the info. I am really hoping the points take care of this. Need to get back fishing again. In the meantime... layball:

 

[Sunken Ship]

I pulled the flywheel this morning sanded the points with 320grit, rinsed with electrical components cleaner, dried with compressed air and then set gap to .020. Sounded great at idle and it took off really strong and as fast as I could think "I fixed it!" it fell on it's face again, so I hit the choke and it took off again. It just couldn't maintain WOT. I then put on the new fuel pump diaphragm while on the water, which made no difference to the engine.

Came home, pulled the carb off and rinsed well with carb/choke cleaner (just put a kit in a couple months ago). Will try again tomorrow to see if the carb cleaning made any difference.

Ignition tune-up kit came this afternoon, will install tomorrow after I test run it. Really curious.

 

[Sunken Ship]

Update:

After cleaning carb. boat ran just as bad, maybe a little worse. Checked fire and lost the bottom cylinder this time-last time it was the top cylinder.

Just installed ignition tune-up kit and said a prayer.

Off to the water. Please cross fingers for me...

 

[Sunken Ship]

Points seems to have helped, but she still falls on her face at WOT. Placed throttle controls to WOT then held choke (manually) flap at about 80% closed and it took off and ran perfectly. The see through fuel filter placed just before the carb. and after the fuel pump is FULL of gas, so it must be something with the carb. Also removed the primer bulb after priming it several times and it ran the same.fuel lines are all nice inside. Got to be something with the carb.

 

[Sunken Ship]

Cleaned carb. thoroughly and that fixed it.

 

[gm280]

Cleaned carb. thoroughly and that fixed it.

It doesn't take much to screw up a jet in a carb... Glad you are going again... :thumb:

 

[Sunken Ship]

Thank you Admiral! I think the motor still has the original Champion plugs. Wondering what plugs you are running? The water port is working great..sure like having it there.

 

[gm280]

In the actually factory shop manual they recommend Champion L4J plugs. I think I ordered mine online but I seriously don't remember what they are now...

 

[Sunken Ship]

I just checked my manual...you were right they are L4J. I had it running really good this last/3rd trip out today and then I lost spark on #2 while sitting at idle fiddling with it, so I pulled the plug and it was fouled. Cleaned and dried with carb/choke cleaner I had aboard and off it went again. Making progress.

Wondering if there is a plug that isn't prone to fouling without chaning the heat range on the plug and causing serious damage to the engine...?

 

[Sunken Ship]

I have it running really good, but it just keeps fouling the plugs now. I can't even idle out of the bay (no wake zone) for 2-3 minutes before the top cylinder is fouled. I am 100% certain the mix is 50:1. I am using 87 with ethanol-going to try ethanol free on tomorrow's run. I even tried some octane boost today, which did not help. Compression is 90 on top and bottom according to my gauge. Gap is .030 on the plugs. I can clean the plugs then run around for 5-10 minutes at 35-40% throttle and the top plug will foul again. I put a new coil on the top cylinder since I have it laying around.

Is clock-wise on the low-speed needle rich and counter is lean? I hate to mess with this as it is idling really good at right around 1 1/4 turns out.

Appreciate any suggestions. Thanks guys.

P.S. Motor is actually a '75, can't edit title.