1968 Evinrude 55hp burning coils

[northface]

I'm about at the end of my coil ... For some reason the engine keeps burning coils. When I install a new one it runs perfect, for a while. Then the coil lets go. The last one ran for 30 min. I list out what I've don to the engine so far.
New Points
New Rotor
New plugs
New power pack
Rewired entire engine
Disconnect the tachometer.

Just can't figure this one out. I've read that coils burn when there is no place for the charge to go. But all the grounds are good. Any thoughts welcome. I hate to part it out. The engine has great compression and runs perfect otherwise.

 

[F_R]

Well it is true that running with a high resistance in the coil-to-distributor-to spark plug circuit forces coil output voltage to go up. Check plug wires for continuity. Could be the rotor, except you replaced that so it isn't that. Correct non-resistor plugs?? Was all that other stuff actually bad, or did you just replace parts while hoping?

 

[northface]

Wires are good. They are pretty new. The rotor is also new but not the distributor.
I replaced these parts because the engine had been sitting for a long time and wires were dry rotted, points pitted.

You had me hopeful with the spark plugs. I just ran down and twisted an old one open ... no resister. The plugs are gapless though, Champion

L76V, which is what the spec calls for. I have wondered if gapless could cause high resistance.​

 

[Tim Frank]

If you replaced the plug wires, hopefully you used metal core wire.
I had the Johnson version of that motor, replaced the plug wires with automotive plug wire and blew the coil. Not actually sure of the mechanism of destruction, but after replacing the coil and the correct plug wires, no problem.

The surface gap plugs were a mixed success and eventually were replaced with QL77JC4 gapped at 0.30"

 

[Faztbullet]

Is it OEM coil or auto style???

 

[northface]

OEM. I've tried both old and new CDI. The older style appear to last longer. Maybe a few months before they start going bad. One of the new CDI actually split at the top. A clear sign they are getting hot, I think.

 

[F_R]

You asked if surface gap plugs increase resistance. The answer is yes. I'd use QL77JC4 gapped at .030". They run better anyway.

 

[northface]

You asked if surface gap plugs increase resistance. The answer is yes. I'd use QL77JC4 gapped at .030". They run better anyway.

Ok, I'll try them. Can surface gap really be enough to burn the coils?

 

[Tim Frank]

No. You are looking for a different root cause to be going through that many coils.
Those were great runners, but first gen of the CDI ignition and could be a challenge sometimes.

You don't say whether this engine is new to you and so the problem is as well, or whether you have had this for a while and the problem just cropped up.

 

[racerone]

Agree with post # 9 here.----There are other problems.----These motors ran with the same coil for years in the late 60' and 1970's

 

[Tim Frank]

What kind of plug wire did you buy?....or maybe a better question, where did you buy them?

 

[northface]

Sorry for the delay, I was bogged down in real life ....

The engine was new to me.The wires were old and cracked (arching) so I replaced them early on. Don't know for sure if this is the root cause.

I can't remember where I got the wires. I thought they were OEMs but can't find the order to confirm. I know the wire from the coil to the dist is the one that came with the coil. I've had both the OEM where the wire is tapped into the coil and the CDI where it's plugged in.

I'll skip the plug idea.

 

[Tim Frank]

Are the plug wires metal core?

 

[northface]

Are the plug wires metal core?

Yes, they are. I also made sure the plugs were the no resistor type. I pulled the distributor and cleaned up the contact areas. The inner contact was a little worn and dirty. I lightly sanded that and the outer contacts to the wires. Checked resistance from the outer to where the plug wires screw in. They all have good continuity. My on-line search for how to test a distributor turned up nothing useful. So this was my best attempt.

Very frustrating. I know it's a wiring issue but I've combed through everything I can find.

There was one item I found that puzzled me. The auto choke is disconnected (I read they were a nightmare and the recommendation was to do this). The wires from the switch to the choke solenoid are set up so it sends 12V to both terminals. Which sets the choke. When I hot this switch it actually sets the ignition and starts to crank the engine. Something definitely screwy there, but this never happened before so I don't think it's the cause of the coil burn. For now I'm disconnecting it.

 

[schematic]

Is it possible the wavy washer is missing above the rotor causing too high a rotor gap?

 

[northface]

No Title

Is it possible the wavy washer is missing above the rotor causing too high a rotor gap?

The washer is there. But I do wonder if the contact on the inner side of the distributor is worn down. Maybe that's creating a gap.

 

[northface]

This is really old thread but I wanted to come back and give an update incase anyone else is having this issue. I finally found some time to really dig and start researching. It appears that since these old motors don't have voltage regulators, they can put out as much as 18V when running at higher RPM. If you mix that with a maintenance free battery (which I am using) you can burn out electrical equipment. I've purchased a new rectifier/regulator and installed. If the coil does not burn out in the next 2-3 months. I'll return and update the post. Hope this was it.

 

[eclipseturbors]

I'm just curious what voltage regulator did you purchase?

 

[northface]

http://www.mfgsupply.com/01-090-1.html

It appears to be working but I haven't had the bout out of the driveway yet. Have my fingers crossed. Pretty frustrating...

 

[eclipseturbors]

Please keep us updated. I'm looking for a voltage regulator now, but may just buy the Harley version.