Magneto timing issue or something else weird?? ('57 SeaKing 25hp)

[singer202]

I first want to thank everyone for their help so far on this project. You have been very helpful but I'm having one final and very odd issue with the motor.

Here's what I know!

Engine torn down and rebuilt.
Good compression on both cylinders.
All electronics (points, condensers, coils, plugs, wires and stop switch) replaced with brand new parts.
Points adjusted to .02 as per service manual.
Plugs gapped properly.
Carb functioning properly.

Symptoms:

The engine is only firing one cylinder.
I pulled the bottom boot while running and the engine died, pulled the top boot and no change. (Therefore the top cyl. is not firing)
HERE'S WHERE IT GETS WEIRD

As I go to put the boot back on the top cylinder while the engine is running, a bright and long arc of electricity jumps from the inside of the boot to the end of the plug and the cylinder begins firing. If I put the boot on, the cylinder dies. Thinking it may be the boot, I removed it, trimmed the wire back, re stripped a new end and replaced the boot. Fire it up and there is no change. I removed the boot again and the spring from the inside of the boot to expose the bare wire. Fire up the engine and move the bare plug wire towards the plug and yield the same results: At about 3/4 of an inch away, the wire arcs to the end of the plug and the cylinder fires, as I move closer or touch the wire to the plug, the arcing stops and the cylinder dies.

I'm kind of stumped at the moment and would love some thoughts or suggestions as to what exactly I should do.

Thanks for any advise!

 

[F_R]

Bad spark plug. Here's a tid-bit of info on the spark. When the breaker points open, a voltage begins to rise in the secondary winding of the coil. It continues to rise until it has someplace to go (across the spark plug gap) or just cannot go any higher due to design limitations. Once the voltage has risen enough, it jumps the spark plug gap and it's all over till the next time. So...when you have the wire off the plug, the voltage continues to rise until it can jump BOTH the distance to the plug AND the plug gap. Meaning you are running an extremely high voltage to the plug. Your plug is failing to fire at normal voltage, but is firing at extremely high voltage. Replace it.

 

[singer202]

Why does the plug work when I am arcing the wire to the end of it but not when the wire is actually connected?

 

[HighTrim]

As Frank stated, higher voltage at that point. Perhaps enough to overcome resistance in plug. Definately try new plugs as he stated.

If not it, I would polish the points to a shine then clean with paper stock dipped in acetone.

 

[F_R]

My previous post was a "in most cases" reply. But I have to say that there also is a possibility that your motor is fouling that seemingly bad plug. Could be excess gas from a ruptured fuel pump diaphragm, water ingestion, excess carbon flaking off and getting in plug, etc.

EDIT: Just as a point of information, there actually are plugs with a built-in gap within the plug, which simulates exactly what you have discovered. Champion identifies such plugs with a "U" leading the type number, such as UL4J. They were developed for motors with inherent fouling problems. But don't try to use them unless the cylinder head and ignition system was designed for them. Yours wasn't.

 

[singer202]

Hey guys. So I feel like a complete schmuck for not catching this but the plugs I have were ordered as part of a complete ignition tune up kit. Apparently they sent me the wrong plugs. What I have are Champions J4C's and my service man. says that I require a J6J. Needless to say, I'm pretty sure I've found my problem. (It turns out that my lawn mower uses a J6J equivalent so I replaced my known dead plug with that and the motor never ran better, well, at first, until my other J4C began acting up. I have a new correct set coming tomorrow. Thanks for the help!

 

[singer202]

Hey guys. So I feel like a complete schmuck for not catching this but the plugs I have were ordered as part of a complete ignition tune up kit. Apparently they sent me the wrong plugs. What I have are Champions J4C's and my service man. says that I require a J6J. Needless to say, I'm pretty sure I've found my problem. (It turns out that my lawn mower uses a J6J equivalent so I replaced my known dead plug with that and the motor never ran better, well, at first, until my other J4C began acting up. I have a new correct set coming tomorrow. Thanks for the help!

 

[nwcove]

not to come across as negative, but there isnt a whole lot of difference between the j4's and the j6's. j4 is better for extended wot running, and j6 is more for trolling and some wot .

 

[singer202]

I've heard they are interchangeable in some applications, but according to the Champion spec sheet, the J6J are hotter and have a different firing end design. I'm hoping that that's my main problem as honestly, I'm confident enough in my rebuild that there is little if anything else it could be. I hope. lol

 

[singer202]

I've also heard of Champion plugs being bad right out of the box, so my new ones will be NGK as well.

 

[HighTrim]

The issue was not the J4C, that motor will run on that. The plug installed was NFG. It happens.

 

[singer202]

Hey guys! So I got a a new set of NGK plugs yesterday and put them in and the motor fired right up and never ran better. It idles nicely, throttle response is good and it sounds great. Now I just gotta wait for this weather to break so I can lake test it. Thanks again for all your help throughout this project!