'76 25hp Evinrude Weak Spark

[sharnholmes]

My 1976 25HP Evinrude has a strong spark (1/2" blue spark) on #1 cyl & a weak spark (1/16" orange spark) on #2 cyl. The strong and weak spark swap cylinders if the ignition wire connectors are swapped just before the ignition coils, so I've seen both ignition coils produce a strong spark. I have replaced the points and condensers and have exactly the same symptom. Is it possible for the driver coil to be defective producing a strong spark on #1 cyl, but not #2? I also thought one magnet might be getting weak on the flywheel, but both are about the same strength when a screwdriver is brought near. I have inspected the wiring between the driver coil/points and the ignition coils and all appears good. There are no visible cracks or deterioration that might create a short to ground. I even disconnected the connectors leading to the kill/off position of the ignition switch to rule out a bad ignition switch.

Any help would be greatly appreciated.

 

[sharnholmes]

Re: '76 25hp Evinrude Weak Spark

I have determined that one of the magnets in the flywheel must be too weak. My model does not have charge coils under the flywheel, so I moved the driver coil 180 degrees to the empty position on the armature plate. This caused the strong and weak spark to swap cyl. In essence this just swapped which magnet was driving which cyl. My new thought is to get a second driver coil and mount both at 180 degrees apart. The leading lead of each driver coil will be mounted at opposite point sets, but the magnets in the flywheel are cast in reverse polarity. My thought is that both driver coils and magnets will work in parallel with each other. This would be cheaper than buying a used flywheel and I wouldn't have to worry about the next flywheel having the same problem as it would be just as old. Has anybody heard of this being done? In theory it sure seems like it would work. Does anybody know of a reason this would not work?

 

[sharnholmes]

Re: '76 25hp Evinrude Weak Spark

I'm new to the forum as this is my first time owning a boat or motor. I sure thought somebody would have chimed in with an opinion about adding a second driver coil under the flywheel. I'm sure this isn't a common practice. Anyhow, I received my second driver coil today and I installed it in the available space 180 degrees from the other driver coil. This put two driver coils and two magnets working in parallel to provide the current and subsequent voltage to cause spark at the plug. Everything worked as planned, both cylinders now have the spark of a brand new engine. I fired it up and it runs like a top, better than it has ever run for me. I can't wait to get it out on the lake. Thank you to those of you who took time to read this thread. I hope this information is helpful to others who may be in the same situation. One note of CAUTION though, I'm sure this ability to add a second driver coil is a very limited situation. Most motors probably don't have room for the second driver coil and different types of ignitions will be engineered differently which may prohibit this type of aftermarket engineering. Thanks again and God bless.

 

[samo_ott]

Re: '76 25hp Evinrude Weak Spark

Wow, that's an interesting upgrade that you did and it worked which is great. Thanks for that info as someone somewhere, sometime will be looking for this info. Do you have a picture of the new ignition system under the flywheel? And welcome to the iboats forum and thanks for contributing to it.

 

[sharnholmes]

Re: '76 25hp Evinrude Weak Spark

It didn't even cross my mind to snap a photo. Next time I pull the flywheel I'll post a picture of it. It might be a while though as the points are new and hopefully the maintenance under the flywheel is done for a while.