Strange Ignition Arcing, 1975 Johnson 9.9 Long Shaft, Electric Start

[awaschka]

I have owned this engine since it was less than one year old. It is used as a sailboat auxiliary.<br />Several years ago it broke a ring and I rebuilt the power head, boring it and adding oversize pistons.<br />There was exceptionally little wear in the lower engine, cross hatching still clearly visible.<br />I have had trouble since getting it to run smoothly and reliably. I have replaced the ignition coils, points and condenser. I have checked the resistance of the driver coil and it is in spec.<br />I think I finally found the rough running problem in that the initial timing was off a little. The ignition was advancing a little before the throttle was opening.<br />At the same time, I noticed that there was a high voltage corona running around the base of the boot on the number one plug.<br />The flashes of the corona were synchronized with misses in the engine. When I pulled the boot off the plug a little to create a gap between the wire and the plug tip the corona disappeared and the engine smoothed out.<br />There are carbon tracks in a ring around the white insulator of the plug.<br />I replaced the plug and all seems to be well, but I don't understand how arcing occurs around the junction between the rubber boot and the ceramic insulator.<br /><br />Anybody seen this before?<br /><br />Thanks,<br /><br />Al<br />

 

[12Footer]

Re: Strange Ignition Arcing, 1975 Johnson 9.9 Long Shaft, Electric Start

I'll give it a stab...The arcing is due to a carbon path. Just like lightning makes it's path to ground, so do these high-falootin,high-voltage ignition systems...They don't call the Merc ignitions "thunderbolt" for nothing, as they can throw an air gap of 1/2" or more!<br />This arcing you have is going to wipe-out the coil, switchbox in quick order, so it's good you found the corona.<br />But back to that (sorry). As high voltage potential is built up to a point of discharge,(spark), it will find the shortest route to earth ground. Salt, dust or moisture in the air, or anything more conductive than air gives it this "shortcut" to ground,hence the arcing. If it arcs enough at the same place, it will burn anything ,even rubber and plastic, and where it does so, form a path of highly conductive carbon (what they make some resistors out of).<br />Kind of like a dripping faucett, it will never stop,and only get worse over time.<br />All you can do to prevent this from re-occuring, is to clean the path off.If you can't, or it's etched-into the coil or wire insulation to the point it cannot be thoroughly removed, it will come back.<br />You can coat the HV system with HV silicone spray, but even this stuff must be cleaned-off,,and re-applied (because it attracts dust and salt contaminants).Which not only defeats the purpose, but makes it worse.<br />Good job at keeping an "eye" on it.

 

[awaschka]

Re: Strange Ignition Arcing, 1975 Johnson 9.9 Long Shaft, Electric Start

I understand what you are saying, but I am seeing a corona around the circumference of the insulator right at the bottom edge of the boot. Its not arcing to ground, i.e. the metallic hex base of the plug. It is almost like it is leaking down the inside of the boot and then arcing through the insulator to the center conductor, but there should be a direct connection from the tip of the plug where the wire connects all the way through the center of the plug. I just don't understand where the arc is going.<br /><br />Al

 

[fireman 757]

Re: Strange Ignition Arcing, 1975 Johnson 9.9 Long Shaft, Electric Start

Hey, 12footer this is not a Merc! The only thing that I can think of awashka is that the coil that fits onto the plug in your plug wire is turned a little bit and is not seated over the tip of your plug. You said that you replace the ignition coil. I just did this on a 35hp Jonnie and you now have to put the things together yourself. Make sure that the plug wire is completely in the coil (almost 1/2") and when you put the coil that goes over the plug in it has a tendency to turn so it will arc to the plug instead of fitting over the cap of the plug. You said it is fine now. Maybe you just didn't have it seated on there all the way.

 

[DJ]

Re: Strange Ignition Arcing, 1975 Johnson 9.9 Long Shaft, Electric Start

awaschka,<br /><br />Possibly, the center electrode in the plug you replaced was broken internally. The current could not take its normal path to the electrode.

 

[Boatist]

Re: Strange Ignition Arcing, 1975 Johnson 9.9 Long Shaft, Electric Start

Awaschka<br />I would like to know what plug you were running. If was a resistor plug like the RL82C it could be internal resistor was open or burned up so you had a internal spark gap inside the insilator. How wide was plug gap, should be .030. Also A cracked plug insolator near the base could cause such a problem.